- reverted removing Libs.private/Requires.private in pkgconfig
files

- enable llvm backend also for ARM

- Add requires for Mesa to Mesa-libGL1 in baselibs.conf
* Mesa required for many applications in wine
* wine-32bit pulls through Mesa-libGL1-32bit without Mesa-32bit

- Remove Requires.private and Libs.private from *.pc files
* Both are needed only for static linking
* This package provides only shared libraries
* the rpm pkgconfig dependency generator considers "Requires.private"
a valid dependency even though there are no static libraries in the
packages
* This cause bloat and hides broken "buildRequires" in other packages.