Remove TOOLCHAIN_LIBS_PATH

The runtime library is now loaded explicitly in
RUNTIME_LIB env variable.
Merge pull request #60 from farcaller/compiler-rt

Remove TOOLCHAIN_LIBS_PATH
Extracted cross-build rustic flags to allow native builds.
Add '--test' flag if building for test.
Added run_tests helper that runs all tests in passed compile_rust rule.
Added 'as_dylib' helper.
Added the very basic platformtree macro code with tests.
Added 'rake test' to travis build.
Allow PIC in native builds.
Allow absolute paths in reps resolver.
Added should_fail flag to compile_rust that reverses exit code.
Small readability cleanup for run_tests.
Added ruby test generator framework.
Added some PT tests that must fail compilation to succeed.
Mute stdout/stderr on failing tests.
Fail if PT path is empty.
Fail if there are trailing tokens after parsing root PT node.
Added a bunch of tests that should fail.
Removed PT debug logging.
Removed unused use imports.