Fix typo

Found by: Duncan P. N. Exon Smith <dexonsmith@apple.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201726 91177308-0d34-0410-b5e6-96231b3b80d8
Avoid collisions with Objective-C++ keywords

Change parameter names exposed in headers to avoid collisions with Objective-C++
keywords.

Contributed-by: Graham Lee <graham@iamleeg.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201727 91177308-0d34-0410-b5e6-96231b3b80d8