[flang] Lowering support for -gdwarf-N flag. (#159137)

This PR builds on the https://github.com/llvm/llvm-project/pull/158314
and adds the lowering support for `-gdwarf-N` flag. The changes to pass
the information to `AddDebugInfo` pass are mostly mechanical. The
`AddDebugInfo` pass adds `ModuleFlagsOp` in the module which gets
translated to correct llvm metadata during mlir->llvmir translation.

There is minor correction where the version is set to 0 in case no
-debug-version flag is provided. Previously it was set to 2 in this case
due to misreading of clang code.

1 files changed, 1 insertions, 2 deletions

diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
index a00e568..4729f8a 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -157,10 +157,9 @@ static bool parseDebugArgs(Fortran::frontend::CodeGenOptions &opts,
           clang::DiagnosticsEngine::Warning, "Unsupported debug option: %0");
       diags.Report(debugWarning) << arg->getValue();
     }
-    // The default value of 2 here is to match clang.
     opts.DwarfVersion =
         getLastArgIntValue(args, clang::driver::options::OPT_dwarf_version_EQ,
-                           /*Default=*/2, diags);
+                           /*Default=*/0, diags);
   }
   return true;
 }