Auto merge of #3102 - nipunn1313:attempt, r=alexcrichton

Auto merge of #3102 - nipunn1313:attempt, r=alexcrichton

Mix feature flags into fingerprint/metadata shorthash

Since building dependencies results in different libraries
depending on the feature flags, I added the feature flags into
the short_hash.

This solves an issue when multiple crates share a target directory
or multiple targets share a common library with divergent feature
flag choice.

I'm not sure if this architecturally the best way to solve this problem, but I did confirm that this fixes the issue I was seeing. I can also add a test for this case if this code is taking the right approach (or if it would help illustrate the issue).