linux, darwin: don't touch environ in uv_setup_args
linux, darwin: don't touch environ in uv_setup_args

Don't overwrite the environment. On OS X, the entries in the environ
table are not necessarily adjacent. It's arguably also safer for setuid
binaries.

Fixes joyent/node#4847.

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