Handle cfg-gated dependencies.

Parsing them properly would be more reliable, but this set of strings
is good enough to handle the 13 crates in AOSP so far which have such
dependencies. Actually in most cases `cfg(unix)` is all we need.

Bug: 299265444
Test: Ran on all existing crates, and 13 with cfg-gated dependencies.
Change-Id: I35c4bac644dee980f4031a592b67dfade3a624d4
1 file changed