meson/llvm: add native for gallium swrast

If we are building llvmpipe and lavapipe we want native in this
list.

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9208>

meson.build

@@ -1515,7 +1515,7 @@ endif
 if with_microsoft_clc
   llvm_modules += ['target', 'linker', 'irreader', 'option', 'libdriver']
 endif
-if with_tests
+if with_tests or with_gallium_softpipe
   llvm_modules += 'native'
 endif