build: re-enable ccache support

The ccache support was mostly disabled because it
didn't hook onto most compilers anymore.

Caveat: ccache and scan-build don't work together since
scan-build doesn't like arguments in its compiler command
line (eg. "ccache gcc").

Change-Id: I7c1c6e22cb662f2b08e774ea484ac1c412fdd2db
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/5775
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
2 files changed