Make error text if clang-format is not on the system PATH more helpful,
as this is going to be a common mistake (installing LLVM defaults to not putting
the tools onto the PATH).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190036 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed