to highlight some changes:
- this gets rid of the bash dependency (after installing)
- osxcross-env, osxcross-conf and (the fake) dsymutil are now implemented
in the wrapper
- added: 'sw_vers' tool, which is required by some projects (llvm, ...)
- added '-oc-use-gcc-libs' option (uses './build_gcc.sh' libstdc++)
This new wrapper is also more restrict and several times faster than the bash
implementation (~0.2ms vs. 10ms+).
