Eliminate redundant MangleBuffer class

The only remaining user didn't actually use the non-dynamic storage facility
this class provides.

The std::string is transitional and likely to be StringRefized shortly.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210058 91177308-0d34-0410-b5e6-96231b3b80d8
Fix -emit-codegen-only to not generate binaries

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210059 91177308-0d34-0410-b5e6-96231b3b80d8