mk: Split target triples into bulid triple + host triples + target triples

For cross compiling to targets that don't want to build a compiler
mk: Refactor platform.mk a bit
submodule: libuv for android
mk: rewrite make files
mk: mingw32 flags added
mk: mingw32 fix
mk: Cross-compile fixes
Allow constant c-like enum to integral/float cast
mk: cleanup - lib and executable suffix handling
replace option::iter with a BaseIter impl
Construct const fns based on the type, not the definition.

Otherwise we can add a null environment when we shouldn't.

Fixes #5210.
Assert that constants are translated with the correct size.
Add a test case for const fn sizing, just to be safe.
mk: rt.mk fix for libuv cross compile
mk: Restore toolchain config for i386 mac/linux, and freebsd

Conflicts:
	mk/platform.mk
mk: platform.mk more flags added
mk: platform.mk typo UNIXY
mk: install/uninstall for multiple target
Change the default level of unused_imports to warn
Remove unused imports throughout src/