[clang] Fix FIXME in dynamic initializer emission, NFCI

This potentially affects platforms that support comdats other than ELF,
COFF, or wasm, but that is the intention of the FIXME, and if they don't
want this behavior, they probably shouldn't advertise comdat support.

Author: rnk

clang/lib/CodeGen/CGDeclCXX.cpp

@@ -640,13 +640,13 @@ CodeGenModule::EmitCXXGlobalVarDeclInitFunc(const VarDecl *D,
       addUsedGlobal(COMDATKey);
     }
 
-    // If we used a COMDAT key for the global ctor, the init function can be
-    // discarded if the global ctor entry is discarded.
-    // FIXME: Do we need to restrict this to ELF and Wasm?
+    // If comdats are in use and supported, place the initializer function into
+    // the comdat group of the global. In the MS ABI, initializers are mangled
+    // and have their own comdat, so we don't include them in the group for
+    // consistency with MSVC.
     llvm::Comdat *C = Addr->getComdat();
-    if (COMDATKey && C &&
-        (getTarget().getTriple().isOSBinFormatELF() ||
-         getTarget().getTriple().isOSBinFormatWasm())) {
+    if (COMDATKey && C && getTriple().supportsCOMDAT() &&
+        !getTarget().getCXXABI().isMicrosoft()) {
       Fn->setComdat(C);
     }
   } else {