Bring r226038 back.

No change in this commit, but clang was changed to also produce trivial comdats when
needed.

Original message:

Don't create new comdats in CodeGen.

This patch stops the implicit creation of comdats during codegen.

Clang now sets the comdat explicitly when it is required. With this patch clang and gcc
now produce the same result in pr19848.

llvm-svn: 226467

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -480,13 +480,13 @@ static unsigned getEncodedLinkage(const GlobalValue &GV) {
   case GlobalValue::ExternalLinkage:
     return 0;
   case GlobalValue::WeakAnyLinkage:
-    return 1;
+    return 16;
   case GlobalValue::AppendingLinkage:
     return 2;
   case GlobalValue::InternalLinkage:
     return 3;
   case GlobalValue::LinkOnceAnyLinkage:
-    return 4;
+    return 18;
   case GlobalValue::ExternalWeakLinkage:
     return 7;
   case GlobalValue::CommonLinkage:
@@ -494,9 +494,9 @@ static unsigned getEncodedLinkage(const GlobalValue &GV) {
   case GlobalValue::PrivateLinkage:
     return 9;
   case GlobalValue::WeakODRLinkage:
-    return 10;
+    return 17;
   case GlobalValue::LinkOnceODRLinkage:
-    return 11;
+    return 19;
   case GlobalValue::AvailableExternallyLinkage:
     return 12;
   }
@@ -629,7 +629,7 @@ static void WriteModuleInfo(const Module *M, const ValueEnumerator &VE,
                               Log2_32_Ceil(MaxGlobalType+1)));
     Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1));      // Constant.
     Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));        // Initializer.
-    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 4));      // Linkage.
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 5));      // Linkage.
     if (MaxAlignment == 0)                                      // Alignment.
       Abbv->Add(BitCodeAbbrevOp(0));
     else {