uv-unix: fix typo in definition of HAVE_PIPE2
uv-unix: fix typo in definition of HAVE_PIPE2

The define HAVE_PIPE2 was always being set, even when the requisites
were not met.

urbit/archaeology2,urbit/archaeology2,unknownbrackets/maxcso,urbit/archaeology2,urbit/archaeology2,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,urbit/archaeology2,urbit/archaeology2,urbit/archaeology2,unknownbrackets/maxcso,urbit/archaeology2,urbit/archaeology2,unknownbrackets/maxcso,unknownbrackets/maxcso