This patch (context diff) and pair of files adds Linux/gcc/gas support
for the libpng Intel MMX optimizations (previously available only for
the MSVC compiler).  Note that the MMX filtering code is not currently
enabled, but the code can still be used and is considerably faster than
the stock C code at decoding interlaced PNG images.

Greg Roelofs
newt@pobox.com
16 February 2000