radeon/llvm: Always build libradeonllvm as static

radeon/llvm: Always build libradeonllvm as static

This library is very small, so there is not much to gain from building
it as a shared library.  Also, when linking statically with LLVM, a
shared libradeonllvm exports LLVM symbols and creates problems when
used with other shared objects that also link statically to LLVM.

Reviewed-by: Mathias.Froehlich@web.de