Assorted minor improvements:

• Add a build conflict for commonmark-cmark-* when DOCS are enabled. This prevents a failure later on in the build. [0]

• Add a new option BE_AMDGPU which can be used to enable the AMDGPU backed used by mesa when BE_NATIVE or BE_FREEBSD is set. Enable this option by default to limit later surprises. [1]

• Use LLVM_ENABLE_Z3_SOLVER instead of the now removed CLANG_ANALYZER_ENABLE_Z3_SOLVER to disable Z3 discovery and linkage.

PR: 239636 [0], 230789 [1]