Revert "targets/opencl: Link against libgallium.la instead of libgallium.a"

Revert "targets/opencl: Link against libgallium.la instead of libgallium.a"

This reverts commit 4148a29ed83d1d85bff3d4e40e847128011c3f20.

This is a work-around for bug:
https://bugs.freedesktop.org/show_bug.cgi?id=59334

We really should be linking against libgallium.la instead of
libgallium.a, but until we can figure why linking against libgallium.la
causes runtime failures in clover we will continue to link against
libgallium.a

Acked-by: Andreas Boll <andreas.boll.dev@gmail.com>
Tested-by: Aaron Watry <awatry@gmail.com>