hg on sparc64

[Ted Unangst]

running hg on sparc64 complains of missing symbols.

t5120$ hg version
python2.7:/usr/local/lib/python2.7/site-packages/mercurial/zstd.so: undefined
symbol '__builtin_bswap32'
python2.7:/usr/local/lib/python2.7/site-packages/mercurial/zstd.so: undefined
symbol '__builtin_bswap64'
Mercurial Distributed SCM (version 4.5.3)