build: use -fvisibility=hidden in autotools build
build: use -fvisibility=hidden in autotools build

The gyp build only exports symbols from the API but the autotools build
did not until now.

Fixes: https://github.com/libuv/libuv/issues/149
PR-URL: https://github.com/libuv/libuv/pull/164
Reviewed-By: Saúl Ibarra Corretgé <8a7991f6950ea189abf159d6ec98d2fcc13dc5f6@gmail.com>

unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso