remove useless attribute visibility from definitions

this was a failed attempt at working around the gcc 3 visibility bug
affecting x86_64. subsequent patch will address it with an ugly but
working hack.

src/internal/libc.c

@@ -7,5 +7,5 @@ struct __libc *__libc_loc()
 	return &__libc;
 }
 #else
-struct __libc __libc ATTR_LIBC_VISIBILITY;
+struct __libc __libc;
 #endif

src/multibyte/internal.c

@@ -23,7 +23,7 @@
              | ( R(0x80,0xc0) >> 12 ) \
              | x )
 
-const uint32_t bittab[] ATTR_LIBC_VISIBILITY = {
+const uint32_t bittab[] = {
 	              C(0x2),C(0x3),C(0x4),C(0x5),C(0x6),C(0x7),
 	C(0x8),C(0x9),C(0xa),C(0xb),C(0xc),C(0xd),C(0xe),C(0xf),
 	D(0x0),D(0x1),D(0x2),D(0x3),D(0x4),D(0x5),D(0x6),D(0x7),