Made GYP file more complete

Bundled some options taken from libuv / v8 / Chromium. It now allows to
build libraries in different architectures:

gyp --depth=. --generator-output output -f make
-Dlibrary=shared_library -Dhost_arch=x64 -Dtarget_arch=x64 sophia.gyp

V=1 make -C output/
Merge pull request #26 from saghul/gyp_fixes

Made GYP file more complete