Remove more superfluous .str() and replace std::string concatenation with Twine.

Following r233392, http://llvm.org/viewvc/llvm-project?rev=233392&view=rev.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233555 91177308-0d34-0410-b5e6-96231b3b80d8
22 files changed