Show directory that was searched for source directory in Clang easyblock

[Flamefire]

(created using eb --new-pr)

[Flamefire]

Test report by @Flamefire

Overview of tested easyconfigs (in order)

• FAIL Clang-13.0.1-GCCcore-11.3.0.eb (build issue)
  (partial log available at https://gist.github.com/Flamefire/32f18f7439838eac3f8b31bf7bc1456a)

Build succeeded for 0 out of 1 (1 easyconfigs in total)
i8019 - Linux Rocky Linux 9.6, x86_64, AMD EPYC 7352 24-Core Processor (zen2), 8 x NVIDIA NVIDIA A100-SXM4-40GB, 580.65.06, Python 3.9.21
See https://gist.github.com/Flamefire/3591197f273c26dea82d85cb9b5bcb22 for a full test report.

This shows the change in a purposely failing build

== 2025-10-15 16:17:37,723 build_log.py:226 ERROR EasyBuild encountered an error (at easybuild/base/exceptions.py:126 in init): Failed to find exactly one source directory in /dev/shm/s3248973-EasyBuild1947937/Clang/13.0.1/GCCcore-11.3.0/libunwind-13.0.1.src for pattern ['compiler-rt-*']: [] (at easybuild/easyblocks/clang.py:261 in find_source_dir)