Improve StringMap unittests: reintroduce move count, but shield against std::pair internals

From: Mehdi Amini <mehdi.amini@apple.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264418 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed