Remove sys::PathSeparator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184852 91177308-0d34-0410-b5e6-96231b3b80d8
Move GetEXESuffix to the one place it is used.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184853 91177308-0d34-0410-b5e6-96231b3b80d8