amd/common: Fix build with new ac_add_function_attr()

amd/common: Fix build with new ac_add_function_attr()

Fix usage of ac_add_function_attr() and make it known!

common/ac_nir_to_llvm.c: In function 'create_llvm_function':
common/ac_nir_to_llvm.c:265:4: error: implicit declaration of function
'ac_add_function_attr' [-Werror=implicit-function-declaration]
    ac_add_function_attr(main_function, i + 1, AC_FUNC_ATTR_BYVAL);
    ^~~~~~~~~~~~~~~~~~~~

Signed-off-by: Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>