ec/curve448: portability fixups.

SPARC condition in __SIZEOF_INT128__==16 is rather performance thing
than portability. Even though compiler advertises int128 capability,
corresponding operations are inefficient, because they are not
directly backed by instruction set.
Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5449)

crypto/ec/curve448/curve448.c

@@ -500,7 +500,7 @@ struct smvt_control {
     int power, addend;
 };
 
-#if defined(__GNUC__) || defined(__clang__)
+#if defined(__GNUC__) && (__GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ > 3))
 # define NUMTRAILINGZEROS	__builtin_ctz
 #else
 # define NUMTRAILINGZEROS	numtrailingzeros

crypto/ec/curve448/curve448utils.h

@@ -23,7 +23,8 @@
  * with arch_arm32.
  */
 # ifndef C448_WORD_BITS
-#  if defined(__SIZEOF_INT128__) && (__SIZEOF_INT128__ == 16)
+#  if (defined(__SIZEOF_INT128__) && (__SIZEOF_INT128__ == 16)) \
+      && !defined(__sparc__)
 #   define C448_WORD_BITS 64      /* The number of bits in a word */
 #  else
 #   define C448_WORD_BITS 32      /* The number of bits in a word */