Remove use of PathV1.h from ExecutionDriver.cpp.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184202 91177308-0d34-0410-b5e6-96231b3b80d8
Remove PathV1.h use from BugDriver.cpp.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184203 91177308-0d34-0410-b5e6-96231b3b80d8
Return a std::string from PrependMainExecutablePath.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184204 91177308-0d34-0410-b5e6-96231b3b80d8