Use the LLVM_GNUC_PREREQ macro instead of the longhand version check

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221219 91177308-0d34-0410-b5e6-96231b3b80d8
[Support][Program] Add findProgramByName(Name, OptionalPaths)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221220 91177308-0d34-0410-b5e6-96231b3b80d8
Use findProgramByName.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221221 91177308-0d34-0410-b5e6-96231b3b80d8