Don't make libmesa.a or libglapi.a depend on asm_subdirs

Don't make libmesa.a or libglapi.a depend on asm_subdirs

Since the asm_subdirs target does not actually create a file, make will
always consider that it needs to be rebuilt. If libmesa.a and libglapi.a
have asm_subdirs as a prerequisite, then they will always need to be
rebuilt, too. The correct order will be preserved by the default target,
though.

This should fix #16358.