Add "memory" as a clobber for bswap inline assembly.

This had been causing Camellia (the only cipher that uses these
macros) to fail when compiling "out-of-the-box" with gcc version
"4.3.3-5ubuntu4".  I think because the compiler had no idea any memory
access was going on in these macros.

Adding "memory" as a clobber solves the problem, but is probably
overkill.  I suspect that if we specify the constraint for y
differently, we could get rid of both "memory" and __volatile__, which
would allow the compiler to optimize much more.

Also, in gcc versions that support it, we should probably use the
bswap builtins instead.

src/headers/tomcrypt_macros.h

@@ -105,13 +105,13 @@ asm __volatile__ (               \
    "bswapq %0     \n\t"          \
    "movq   %0,(%1)\n\t"          \
    "bswapq %0     \n\t"          \
-      ::"r"(x), "r"(y));
+   ::"r"(x), "r"(y): "memory");
 
 #define LOAD64H(x, y)          \
 asm __volatile__ (             \
    "movq (%1),%0\n\t"          \
    "bswapq %0\n\t"             \
-   :"=r"(x): "r"(y));
+   :"=r"(x): "r"(y): "memory");
 
 #else