Add support for ${pwd} for -L, -resource-dir and INCLUDE env var

[ArchangelX360]

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[illicitonion]

This looks good, thanks! Please could you expand the tests in test/cargo_build_script/cc_args_and_env/cc_args_and_env_test.bzl to cover these extra args?

[ArchangelX360]

@illicitonion Added tests for both commits, and fixed a couple of bugs. I also merged both logic (equal vs. rest) now given I needed to reason about equal signed variant.

[ArchangelX360]

Anything blocking that to be merged?

[keith]

I just hit this with -resource-dir and verified this patch fixes my case too

[illicitonion]

Sorry for the delay here, it's been a busy few weeks! This LGTM, thanks so much for the tests (and fixes), this looks great!