Enable compat build for llvm7 transistion (by lakostis@)

mipsel: add "mipsel-alt-linux" to the triplets list.

Build with gcc on mipsel.

llvm-ar: backported support of dashed options (chromium build

aarch64: rebuilt with clang.

lld: backported upstream commit implementing --{push,pop}-state support.
clang: changed default dynamic linker path for aarch64 architecture.
aarch64: temporarily rebuilt with gcc to fix build from source.
clang-alt-triple.patch: added mipsel and mips64el triplets.

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).