unix: Support Android libuv standalone build

Tested most of my compilation in the previous patch on NodeJS
and extracted the patches from there. This additional patch ensures 
libuv will be capable of building standalone as well, both with gyp
and Makefiles.

Build documentation was added to the README.md file.

Some tests are failing, and I have not heavily investigated
the reasons. The failures are generally on error-conditions, and are
likely related to differences between fully POSIX-compatible
systems and android. Resolving these failures should logically
be done in separate bug reports and is currently out of scope
for my work on uv and node.