FIx comments of createReplaceableForwardDecl() and createForwardDecl().

[friss]

Summary

Noticed while trying to understand how the merge of forward decalred types
and defintions work.

[aprantl]

Looks good to me.

[friss]

Closed by commit rL217514 (authored by @friss).

lib/IR/DIBuilder.cpp

 }
 
 /// createUnspecifiedParameter - Create unspeicified type descriptor
 /// for the subroutine type.
 DIBasicType DIBuilder::createUnspecifiedParameter() {
   return DIBasicType();
 }
 
-/// createForwardDecl - Create a temporary forward-declared type that
-/// can be RAUW'd if the full type is seen.
+/// createForwardDecl - Create a permanent forward-declared type.
 DICompositeType
 DIBuilder::createForwardDecl(unsigned Tag, StringRef Name, DIDescriptor Scope,
                              DIFile F, unsigned Line, unsigned RuntimeLang,
                              uint64_t SizeInBits, uint64_t AlignInBits,
                              StringRef UniqueIdentifier) {
   // Create a temporary MDNode.
   Value *Elts[] = {
     GetTagConstant(VMContext, Tag),
DIBuilder::createForwardDecl(unsigned Tag, StringRef Name, DIDescriptor Scope,
   DICompositeType RetTy(Node);
   assert(RetTy.isCompositeType() &&
          "createForwardDecl result should be a DIType");
   if (!UniqueIdentifier.empty())
     retainType(RetTy);
   return RetTy;
 }
 
-/// createForwardDecl - Create a temporary forward-declared type that
+/// createReplaceableForwardDecl - Create a temporary forward-declared type that
 /// can be RAUW'd if the full type is seen.
 DICompositeType DIBuilder::createReplaceableForwardDecl(
     unsigned Tag, StringRef Name, DIDescriptor Scope, DIFile F, unsigned Line,
     unsigned RuntimeLang, uint64_t SizeInBits, uint64_t AlignInBits,
     StringRef UniqueIdentifier) {
   // Create a temporary MDNode.
   Value *Elts[] = {
     GetTagConstant(VMContext, Tag),