ADT: Use LLVM_NODISCARD instead of LLVM_ATTRIBUTE_UNUSED_RESULT for StringRef

Instead of annotating (most of) the StringRef API, we can just
annotate the type directly. This is less code and it will warn in more
cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284364 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed