Makefile: enforce target name in generated dependencies

Due to the current ccache version's bug need to explicitly request gcc
to set the generated .d file's targets to include the path to the .o
file.

BUG=b:148943341
TEST=verified that relevant object files are rebuilt when an .h file
     is touched.

Change-Id: Ifbe48c191f8585f40da4eac1db29c44f4686c5c3
1 file changed