Fix a configure issue with Visual Studio generators.

Fix a configure issue with Visual Studio generators.

We can't put the unittest source dir map in the configuration
specific directory because VS doesn't have a configure-specific
directory, instead it only knows this at runtime.  So we have
to remove this from the path.  This in turn means that the path
will be slightly different in VS configurations vs non vs
configurations.  In the former, the source map will be in the
parent directory of the executable, and in the latter it will
be in the same directory as the executable.  So check both.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@341590 91177308-0d34-0410-b5e6-96231b3b80d8