[HIP] Tighten checks in hip-include-path.hip test case

The checks (both positive and negative checks) in the test case
hip-include-path.hip could mistakenly end up matching the string
"clang" from the InstalledDir in case the build dir for example
was named "/home/username/build-clang/". Intention with this
patch is to tighten up the checks a bit to filter our the
part of the paths that match with InstalledDir when doing the
checks, as well as matching "/lib/clang/" rather than
just "clang/".

Problem was found when building with
  -DCLANG_DEFAULT_RTLIB=compiler-rt
  -DCLANG_DEFAULT_CXX_STDLIB=libc++
and having "clang/" in the path to the build dir.

Reviewed By: yaxunl

Differential Revision: https://reviews.llvm.org/D102723