According to patch author GCC can optimize expressions like
"(a<<8)|(a>>8)", but has problems with "(a<<8)+(a>>8)".
Patch-from: lvqcl <lvqcl.mail@gmail.com>
Versions of GCC prior to 4.8 didn't provide an implementation
of __builtin_bswap16 on x86_64. Detect those versions and
supply a fallback implementation. A cleaner fix would be
to detect bswap16 independently of bswap32 in configure
and handle them separately.
See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52624
Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
