rustc: android cross compilation

rustc - android cross compilation with `--target=arm-unknown-android` option

it also has cmake build system to build rustc and runtime libraries for target.

libuv for android is on git://github.com/ILyoan/libuv.git


it has some known problems yet
- rustrt for android does not use morestack
- compiling libcore with -O option cause a segmentation fault on android