Fix missing code map entry for uses of `include_str!`.
Add --dep-info to write Makefile-compatible dependency info.

When --dep-info is given, rustc will write out a `$input_base.d` file in the
output directory that contains Makefile compatible dependency information for
use with tools like make and ninja.
Add test for --dep-info.
auto merge of #10698 : metajack/rust/dep-info, r=alexcrichton

This isn't super useful for libraries yet without #10593.

Fixes #7633.