Revised wording for diagnostics in r208299


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208401 91177308-0d34-0410-b5e6-96231b3b80d8
Permit duplicate explicit class instantiations if MSVCCompat is enabled

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208402 91177308-0d34-0410-b5e6-96231b3b80d8