Reduce usage of sys::Path in the graph writer.

Now PathV1.h is not needed in GraphWriter.h.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183919 91177308-0d34-0410-b5e6-96231b3b80d8
Update code for other graph viewing programs too.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183920 91177308-0d34-0410-b5e6-96231b3b80d8
Covert remaining graph viewers from sys::Path to std::string.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183921 91177308-0d34-0410-b5e6-96231b3b80d8