meson: fix gcc vector 64-bit check
the previous behavior only ever enabled gcc vectors no x86_64
@@ -328,7 +328,7 @@ if get_option('gcc_vector')
# error "GCC vector intrinsics are disabled on GCC prior to 4.9"
# elif defined(__arm__)
# error "GCC vector intrinsics are disabled on ARM"
-# elif !defined(__x86_64__)
+# elif (__SIZEOF_POINTER__ < 8)
# error "GCC vector intrinsics are disabled on 32bit"
# endif
#else
