kbuild: add CONFIG_ASM_MODVERSIONS

Add CONFIG_ASM_MODVERSIONS. This allows to remove one if-conditional
nesting in scripts/Makefile.build.

scripts/Makefile.build is run every time Kbuild descends into a
sub-directory. So, I want to avoid $(wildcard ...) evaluation
where possible although computing $(wildcard ...) is so cheap that
it may not make measurable performance difference.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/Kconfig

@@ -14,6 +14,7 @@ config M68K
 	select DMA_DIRECT_REMAP if HAS_DMA && MMU && !COLDFIRE
 	select HAVE_IDE
 	select HAVE_AOUT if MMU
+	select HAVE_ASM_MODVERSIONS
 	select HAVE_DEBUG_BUGVERBOSE
 	select GENERIC_IRQ_SHOW
 	select GENERIC_ATOMIC64