renaming of LLVM runtime library packages

[Matthias Klose]

Hi Samuel,

you are the only maintainer depending on one of the renamed runtime 
libraries in llvm-toolchain-21 (libc++1, libc++abi1, llvm-libunwind1, 
libomp5).

Please have a look if eztrace and starpu, if these build and work, and 
then please try to run these with the libomp5 from experimental (LLVM 
22) to see if they still work.

Thanks, Matthias