[CodeGen] Clarify comment about COFF common symbol alignment

[smeenai]

Summary

After a discussion on the commit thread, it seems the 32 byte alignment
limitation is an MSVC toolchain artifact, not an inherent COFF
restriction. Clarify the comment accordingly, since saying COFF in the
comment but using isKnownWindowsMSVCEnvironment in the conditional is
confusing. Also add a newline before the comment, which is consistent
with the local style.

[majnemer]

lib/CodeGen/CodeGenModule.cpp

3765–3766

I think it is most clear if this comment said "Microsoft's link.exe" instead of MSVC.

[smeenai]

Refer to link.exe, and then also refer to other linkers in the second half of the comment to match

[mstorsjo]

LGTM

lib/CodeGen/CodeGenModule.cpp

if (const auto *RT = VarType->getAs<RecordType>()) {
           continue;
         if (FD->hasAttr<AlignedAttr>())
           return true;
         if (Context.isAlignmentRequired(FD->getType()))
           return true;
       }
     }
   }
-  // COFF doesn't support alignments greater than 32, so these cannot be
-  // in common.
+
+  // MSVC doesn't support alignments greater than 32 for common symbols, so
+  // symbols with greater alignment requirements cannot be common. Non-MSVC COFF
+  // environments support arbitrary power-of-two alignments for common symbols
+  // via the aligncomm directive, so the restriction doesn't apply there.
   if (Context.getTargetInfo().getTriple().isKnownWindowsMSVCEnvironment() &&
       Context.getTypeAlignIfKnown(D->getType()) > 32)
     return true;
 
   return false;
 }
 
 llvm::GlobalValue::LinkageTypes CodeGenModule::getLLVMLinkageForDeclarator(