int128: move __uint128_t compiler test to Kconfig

In order to use 128-bit integer arithmetic in C code, the architecture
needs to have declared support for it by setting ARCH_SUPPORTS_INT128,
and it requires a version of the toolchain that supports this at build
time. This is why all existing tests for ARCH_SUPPORTS_INT128 also test
whether __SIZEOF_INT128__ is defined, since this is only the case for
compilers that can support 128-bit integers.

Let's fold this additional test into the Kconfig declaration of
ARCH_SUPPORTS_INT128 so that we can also use the symbol in Makefiles,
e.g., to decide whether a certain object needs to be included in the
first place.

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/lib/ubsan.h b/lib/ubsan.h
index b8fa838..7b56c09 100644
--- a/lib/ubsan.h
+++ b/lib/ubsan.h
@@ -78,7 +78,7 @@ struct invalid_value_data {
 	struct type_descriptor *type;
 };
 
-#if defined(CONFIG_ARCH_SUPPORTS_INT128) && defined(__SIZEOF_INT128__)
+#if defined(CONFIG_ARCH_SUPPORTS_INT128)
 typedef __int128 s_max;
 typedef unsigned __int128 u_max;
 #else