Make BuiltinType::getName return a StringRef and introduce BuiltinType::getNameAsCString
to get a const char* if necessary.

This avoids unnecessary conversions when we want to use the result of getName as
a StringRef.

Part of rdar://10796159

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@156227 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed