Move PrependMainExecutablePath next to its only user.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183980 91177308-0d34-0410-b5e6-96231b3b80d8
Remove a use of PathV1.h.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183982 91177308-0d34-0410-b5e6-96231b3b80d8