Use dependency files generated by llvm-rs-cc

This was a regression since kati has been introduced. This CL
introduces include-depfile function to make it easier to write
Makefiles which work with both make and kati.

As ninja can handle only a single dependency file per a build
rule, now we merge multiple .d files generated by llvm-rs-cc
into a .d file.

Change-Id: Iaf64a8f0523ab98115837e6e06abd50f06620363