Add ability to run build-time tests #4789

Historically, most ROCm tests get built standalone and then distributed to GPU runners for execution. But there are a number of projects which (correctly) have CPU-side unit tests intended to be run from the build tree. We want to support these with a new therock_subproject_build_test() directive that:

• Adds test stamps and wires up the command to execute in the build graph
• Only runs for built projects (skips for prebuilt)
• Is excluded from ALL and must be explicitly invoked via build-test-foo or build-tests targets.

While implementing this, it was attempted to enable the KPACK C++ unit tests but they have an issue that was not caught in the standalone pre-submits:

  [1/2] Linking CXX executable runtime/tests/test_kpack_runtime
  /usr/bin/ld: runtime/tests/CMakeFiles/test_kpack_runtime.dir/test_isa_target_match.cpp.o:
  undefined reference to `kpack::parse_target_id(std::__cxx11::basic_string<char, ...> const&)'
  /usr/bin/ld: runtime/tests/CMakeFiles/test_kpack_runtime.dir/test_isa_target_match.cpp.o:
  undefined reference to `kpack::strip_target_prefix[abi:cxx11](char const*)'
  collect2: error: ld returned 1 exit status

Cause/solution:

• Cause: test_isa_target_match.cpp white-box tests internal helpers from runtime/src/isa_target_match.cpp, but test_kpack_runtime only links runtime/librocm_kpack.so.0.1.0. In TheRock’s shared-library build those internal helper symbols are not available to the test executable.
• Confirmed fix: adding ../src/isa_target_match.cpp to test_kpack_runtime sources makes the test executable link, and then kpack CTest passes 101/101. I backed that fix out per request.

Landing this facility with the KPACK unit tests commented out. We should hold this issue open until that is resolved and they are enabled.