Add a function to match modules through a variation map.

Can be a more convenient alternative than specifying the full subdir
concatenation of the variants. E.g. common arch and os variations don't
have to be hardcoded.

Test: `m nothing` with https://r.android.com/1801128
Change-Id: Ic2966e109d61dfee6a2b4fcbcbf8f73274babca9