ci: use venv amdclang++ and bump stable pin to 7.14.0a20260616

whl-multi-arch converts symlinks to hardlinks during install. After
rocm-sdk init, _rocm_sdk_devel/bin/amdclang++ is a hardlink whose
exec stub resolves siblings via /proc/self/exe — it looks for
_rocm_sdk_devel/bin/amdllvm, which was absent in all whl packages
before 7.14.0a20260616 (TheRock PR #5810 / issue #5726).

Switch CXX from {rocm}/bin/amdclang++ to {venv}/bin/amdclang++.
The venv path is a pip entry point that calls os.execv directly on
lib/llvm/bin/amdclang++, where amdllvm has always existed. This
makes the CI immune to future regressions of the same class.

Also bump the stable pin to 7.14.0a20260616, the first version that
includes the upstream amdllvm fix in the whl package itself.

Co-Authored-By: Claude Sonnet 4 <noreply@anthropic.com>

Author: mapatel-amd

.github/build_tools/stable_rocm_version.txt

@@ -1 +1 @@
-7.14.0a20260613
+7.14.0a20260616

.github/workflows/build-rocm-examples-reusable.yml

@@ -164,7 +164,7 @@ jobs:
               f.write(f"LIBRARY_PATH={rocm}/lib:{rocm}/lib64\n")
               f.write(f"LD_LIBRARY_PATH={core}:{libs}:{rocm}/lib:{rocm}/llvm/lib\n")
               f.write("ENABLE_OPENMP=OFF\n")  # whl-multi-arch omits amdllvm needed for OpenMP GPU offloading
-              f.write(f"CXX={rocm}/bin/amdclang++\n")  # hipDNN headers require C++20; system g++ on AlmaLinux 8 is too old
+              f.write(f"CXX={venv}/bin/amdclang++\n")  # hipDNN headers require C++20; system g++ on AlmaLinux 8 is too old
           rocm_version = subprocess.check_output(["rocm-sdk", "version"], text=True).strip()
           with open(github_output, "a") as f:
               f.write(f"rocm_version={rocm_version}\n")