[Arm64EC] Copy import descriptors to the EC Map (#84834)

As noted in <https://github.com/llvm/llvm-project/pull/78537>, MSVC
places import descriptors in both the EC and regular map - that PR moved
the descriptors to ONLY the regular map, however this causes linking
errors when linking as Arm64EC:

```
bcryptprimitives.lib(bcryptprimitives.dll) : error LNK2001: unresolved external symbol __IMPORT_DESCRIPTOR_bcryptprimitives (EC Symbol)
```

This change copies import descriptors from the regular map to the EC
map, which fixes this linking error.

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/Object/ArchiveWriter.cpp b/llvm/lib/Object/ArchiveWriter.cpp
index be51093..e062974 100644
--- a/llvm/lib/Object/ArchiveWriter.cpp
+++ b/llvm/lib/Object/ArchiveWriter.cpp
@@ -677,6 +677,13 @@ static bool isECObject(object::SymbolicFile &Obj) {
   return false;
 }
 
+bool isImportDescriptor(StringRef Name) {
+  return Name.starts_with(ImportDescriptorPrefix) ||
+         Name == StringRef{NullImportDescriptorSymbolName} ||
+         (Name.starts_with(NullThunkDataPrefix) &&
+          Name.ends_with(NullThunkDataSuffix));
+}
+
 static Expected<std::vector<unsigned>> getSymbols(SymbolicFile *Obj,
                                                   uint16_t Index,
                                                   raw_ostream &SymNames,
@@ -704,6 +711,10 @@ static Expected<std::vector<unsigned>> getSymbols(SymbolicFile *Obj,
       if (Map == &SymMap->Map) {
         Ret.push_back(SymNames.tell());
         SymNames << Name << '\0';
+        // If EC is enabled, then the import descriptors are NOT put into EC
+        // objects so we need to copy them to the EC map manually.
+        if (SymMap->UseECMap && isImportDescriptor(Name))
+          SymMap->ECMap[Name] = Index;
       }
     } else {
       Ret.push_back(SymNames.tell());