Backport fixes to p8 branch.

Backport to p8 branch.

Reduce debuginfo for x86_64.
Use 'Release' build on x86_64.
Fix provides/obsoletes.
Move clang libs to separate pkg (to ease future migrations).

Bootstrap with clang, lld and ThinLTO.
.spec: sync with RH
DebugInfo-Discard-invalid-DBG_VALUE-instructions-in-.patch
Fixup-for-rL326769-RegState-Debug-is-being-truncated.patch
0001-CMake-Split-static-library-exports-into-their-own-ex.patch
.spec: move gold plugin to -devel (tnx to legion@)
Build changes:
g1)
rt (instead of libgcc).

Test build using clang and lld.
Increase build jobs number to 16 (thanks to lld/thinLTO).

Prepare for LLD/clang build bootstrap.

Added LLD build.

Added flag to build with clang (should reduce memory usage for LTO).
Reduce build jobs (workaround to reduce memory consumption).

Updated to 6.0.0 release.
Build changes:

Replaced X86 with native in the list of targets.
Added provides and obsoletes to replace old llvm packages and its

NMU: changed CMake Modules install path

remove conflicts: llvm from -libs pkg (closes #33879).

Updated 4.0.0 release and build configuration:

Installed example llvm plugins required by cmake modules.

Define cmake modules dir correctly (closes #33250).

Updated 4.0.0 release.