Better error code when lacking __SIZEOF_INT128__

Fixes #6327
Reviewed-by: NAndy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6328)

crypto/ec/ecp_nistp224.c

@@ -45,7 +45,7 @@ NON_EMPTY_TRANSLATION_UNIT
 typedef __uint128_t uint128_t;  /* nonstandard; implemented by gcc on 64-bit
                                  * platforms */
 # else
-#  error "Need GCC 4.0 or later to define type uint128_t"
+#  error "Your compiler doesn't appear to support 128-bit integer types"
 # endif
 
 typedef uint8_t u8;

crypto/ec/ecp_nistp256.c

@@ -47,7 +47,7 @@ typedef __uint128_t uint128_t;  /* nonstandard; implemented by gcc on 64-bit
                                  * platforms */
 typedef __int128_t int128_t;
 # else
-#  error "Need GCC 4.0 or later to define type uint128_t"
+#  error "Your compiler doesn't appear to support 128-bit integer types"
 # endif
 
 typedef uint8_t u8;

crypto/ec/ecp_nistp521.c

@@ -45,7 +45,7 @@ NON_EMPTY_TRANSLATION_UNIT
 typedef __uint128_t uint128_t;  /* nonstandard; implemented by gcc on 64-bit
                                  * platforms */
 # else
-#  error "Need GCC 4.0 or later to define type uint128_t"
+#  error "Your compiler doesn't appear to support 128-bit integer types"
 # endif
 
 typedef uint8_t u8;