Setting `CLANG_DEFAULT_PIE_ON_LINUX` when building clang

It seems that the behaviour for whether or not -fPIE is on by default in Linux changed in clang 14 to be controlled by a flag when building clang:

https://github.com/llvm/llvm-project/commit/1042de90589c74c6998c127d1ee1b33ff3efb8cc

We were having a bit of an issue switching to the 2024 OS CI images and building with clang++ on the OpenVDB project (when moving from 2022 clang11 to the 2024 image):

https://github.com/AcademySoftwareFoundation/openvdb/pull/1926

Shall we set `CLANG_DEFAULT_PIE_ON_LINUX` to match the behaviour of gcc?

Start by tracing the clang build configuration in aswf-docker, then compare the Linux PIE behavior introduced by the linked LLVM commit with the OpenVDB CI issue and the GCC behavior described here. Done means the clang build uses the intended default PIE setting and the affected OpenVDB-style build succeeds on the newer image.

Written by the indexing model from the issue text.