Revert "[flang] Add & use a better visit()"

This reverts commit 2ab9990c9eb79682a4d4b183dfbc7612d3e55328. It has
caused multiple build failures:
*  https://lab.llvm.org/buildbot/#/builders/177/builds/4346
*  https://lab.llvm.org/buildbot/#/builders/180/builds/3803
*  https://lab.llvm.org/buildbot/#/builders/175/builds/10419
*  https://lab.llvm.org/buildbot/#/builders/191/builds/4318
*  https://lab.llvm.org/buildbot/#/builders/173/builds/4274
*  https://lab.llvm.org/buildbot/#/builders/181/builds/4297

All these bots failed with a time-out:
```
command timed out: 1200 seconds without output running [b'ninja', b'-j', b'32'], attempting to kill
```
I'm guessing that that's due to template instantiations failing at some
point (https://reviews.llvm.org/D122441 introduced a custom
implementation of std::visit). Everything seems fine when either:
* building on X86 with GCC or Clang (tested with GCC 9.3 and Clang 12)
* building on AArch64 with GCC (tested with GCC 11)

1 files changed, 89 insertions, 90 deletions

diff --git a/flang/lib/Semantics/mod-file.cpp b/flang/lib/Semantics/mod-file.cpp
index d19dc5c..10d56b2 100644
--- a/flang/lib/Semantics/mod-file.cpp
+++ b/flang/lib/Semantics/mod-file.cpp
@@ -257,74 +257,73 @@ static llvm::raw_ostream &PutGenericName(
 // procedures, type-bound generics, final procedures) which go to typeBindings.
 void ModFileWriter::PutSymbol(
     llvm::raw_ostream &typeBindings, const Symbol &symbol) {
-  common::visit(
-      common::visitors{
-          [&](const ModuleDetails &) { /* should be current module */ },
-          [&](const DerivedTypeDetails &) { PutDerivedType(symbol); },
-          [&](const SubprogramDetails &) { PutSubprogram(symbol); },
-          [&](const GenericDetails &x) {
-            if (symbol.owner().IsDerivedType()) {
-              // generic binding
-              for (const Symbol &proc : x.specificProcs()) {
-                PutGenericName(typeBindings << "generic::", symbol)
-                    << "=>" << proc.name() << '\n';
-              }
-            } else {
-              PutGeneric(symbol);
-              if (x.specific()) {
-                PutSymbol(typeBindings, *x.specific());
-              }
-              if (x.derivedType()) {
-                PutSymbol(typeBindings, *x.derivedType());
-              }
-            }
-          },
-          [&](const UseDetails &) { PutUse(symbol); },
-          [](const UseErrorDetails &) {},
-          [&](const ProcBindingDetails &x) {
-            bool deferred{symbol.attrs().test(Attr::DEFERRED)};
-            typeBindings << "procedure";
-            if (deferred) {
-              typeBindings << '(' << x.symbol().name() << ')';
-            }
-            PutPassName(typeBindings, x.passName());
-            auto attrs{symbol.attrs()};
-            if (x.passName()) {
-              attrs.reset(Attr::PASS);
-            }
-            PutAttrs(typeBindings, attrs);
-            typeBindings << "::" << symbol.name();
-            if (!deferred && x.symbol().name() != symbol.name()) {
-              typeBindings << "=>" << x.symbol().name();
-            }
-            typeBindings << '\n';
-          },
-          [&](const NamelistDetails &x) {
-            decls_ << "namelist/" << symbol.name();
-            char sep{'/'};
-            for (const Symbol &object : x.objects()) {
-              decls_ << sep << object.name();
-              sep = ',';
-            }
-            decls_ << '\n';
-          },
-          [&](const CommonBlockDetails &x) {
-            decls_ << "common/" << symbol.name();
-            char sep = '/';
-            for (const auto &object : x.objects()) {
-              decls_ << sep << object->name();
-              sep = ',';
-            }
-            decls_ << '\n';
-            if (symbol.attrs().test(Attr::BIND_C)) {
-              PutAttrs(decls_, symbol.attrs(), x.bindName(), ""s);
-              decls_ << "::/" << symbol.name() << "/\n";
-            }
-          },
-          [](const HostAssocDetails &) {},
-          [](const MiscDetails &) {},
-          [&](const auto &) { PutEntity(decls_, symbol); },
-      },
+  std::visit(common::visitors{
+                 [&](const ModuleDetails &) { /* should be current module */ },
+                 [&](const DerivedTypeDetails &) { PutDerivedType(symbol); },
+                 [&](const SubprogramDetails &) { PutSubprogram(symbol); },
+                 [&](const GenericDetails &x) {
+                   if (symbol.owner().IsDerivedType()) {
+                     // generic binding
+                     for (const Symbol &proc : x.specificProcs()) {
+                       PutGenericName(typeBindings << "generic::", symbol)
+                           << "=>" << proc.name() << '\n';
+                     }
+                   } else {
+                     PutGeneric(symbol);
+                     if (x.specific()) {
+                       PutSymbol(typeBindings, *x.specific());
+                     }
+                     if (x.derivedType()) {
+                       PutSymbol(typeBindings, *x.derivedType());
+                     }
+                   }
+                 },
+                 [&](const UseDetails &) { PutUse(symbol); },
+                 [](const UseErrorDetails &) {},
+                 [&](const ProcBindingDetails &x) {
+                   bool deferred{symbol.attrs().test(Attr::DEFERRED)};
+                   typeBindings << "procedure";
+                   if (deferred) {
+                     typeBindings << '(' << x.symbol().name() << ')';
+                   }
+                   PutPassName(typeBindings, x.passName());
+                   auto attrs{symbol.attrs()};
+                   if (x.passName()) {
+                     attrs.reset(Attr::PASS);
+                   }
+                   PutAttrs(typeBindings, attrs);
+                   typeBindings << "::" << symbol.name();
+                   if (!deferred && x.symbol().name() != symbol.name()) {
+                     typeBindings << "=>" << x.symbol().name();
+                   }
+                   typeBindings << '\n';
+                 },
+                 [&](const NamelistDetails &x) {
+                   decls_ << "namelist/" << symbol.name();
+                   char sep{'/'};
+                   for (const Symbol &object : x.objects()) {
+                     decls_ << sep << object.name();
+                     sep = ',';
+                   }
+                   decls_ << '\n';
+                 },
+                 [&](const CommonBlockDetails &x) {
+                   decls_ << "common/" << symbol.name();
+                   char sep = '/';
+                   for (const auto &object : x.objects()) {
+                     decls_ << sep << object->name();
+                     sep = ',';
+                   }
+                   decls_ << '\n';
+                   if (symbol.attrs().test(Attr::BIND_C)) {
+                     PutAttrs(decls_, symbol.attrs(), x.bindName(), ""s);
+                     decls_ << "::/" << symbol.name() << "/\n";
+                   }
+                 },
+                 [](const HostAssocDetails &) {},
+                 [](const MiscDetails &) {},
+                 [&](const auto &) { PutEntity(decls_, symbol); },
+             },
       symbol.details());
 }
 
@@ -595,7 +594,7 @@ void CollectSymbols(
 }
 
 void ModFileWriter::PutEntity(llvm::raw_ostream &os, const Symbol &symbol) {
-  common::visit(
+  std::visit(
       common::visitors{
           [&](const ObjectEntityDetails &) { PutObjectEntity(os, symbol); },
           [&](const ProcEntityDetails &) { PutProcEntity(os, symbol); },
@@ -1106,27 +1105,27 @@ void SubprogramSymbolCollector::DoSymbol(
   if (!needSet_.insert(symbol).second) {
     return; // already done
   }
-  common::visit(common::visitors{
-                    [this](const ObjectEntityDetails &details) {
-                      for (const ShapeSpec &spec : details.shape()) {
-                        DoBound(spec.lbound());
-                        DoBound(spec.ubound());
-                      }
-                      for (const ShapeSpec &spec : details.coshape()) {
-                        DoBound(spec.lbound());
-                        DoBound(spec.ubound());
-                      }
-                      if (const Symbol * commonBlock{details.commonBlock()}) {
-                        DoSymbol(*commonBlock);
-                      }
-                    },
-                    [this](const CommonBlockDetails &details) {
-                      for (const auto &object : details.objects()) {
-                        DoSymbol(*object);
-                      }
-                    },
-                    [](const auto &) {},
-                },
+  std::visit(common::visitors{
+                 [this](const ObjectEntityDetails &details) {
+                   for (const ShapeSpec &spec : details.shape()) {
+                     DoBound(spec.lbound());
+                     DoBound(spec.ubound());
+                   }
+                   for (const ShapeSpec &spec : details.coshape()) {
+                     DoBound(spec.lbound());
+                     DoBound(spec.ubound());
+                   }
+                   if (const Symbol * commonBlock{details.commonBlock()}) {
+                     DoSymbol(*commonBlock);
+                   }
+                 },
+                 [this](const CommonBlockDetails &details) {
+                   for (const auto &object : details.objects()) {
+                     DoSymbol(*object);
+                   }
+                 },
+                 [](const auto &) {},
+             },
       symbol.details());
   if (!symbol.has<UseDetails>()) {
     DoType(symbol.GetType());