Use --crate-file-name to find out the library filename in dep-info test
Allow optional filename argument for --dep-info
auto merge of #11046 : zargony/rust/dep-info, r=alexcrichton

Using --dep-info writes Makefile-compatible dependency info to a file that is by default named based on the crate source filename. This PR adds an optional string argument to the --dep-info option which allows to write dependency info to an arbitrary filename.

cc #10698
cc @metajack