External usage improvements
Add the ability to override where the wrapper scripts look for things so the toolchain can be used from an exported Piksi SDK.
$ shasum -a 256 llvm-obfuscator-arm-x86.txz
8cdfe66e829073fdfdbccd9bf9b83e3ca0add713bb3b924056bf3815be7a2cc6 llvm-obfuscator-arm-x86.txz