Makefile.inc: Export CCACHE_EXTRAFILES and add __BUILD_DIR__ definition

This patch adds the CCACHE_EXTRAFILES variable to the list of exported
environment variables, which can be useful as a target-specific variable
to make ccache aware of extra dependencies that it cannot figure out on
its own. It also adds a CPPFLAGS parameter to define the __BUILD_DIR__
constant for the preprocessor so that the current output build directory
can be referenced in C code if necessary.

Change-Id: I4fdd08842972cfed8ef5e5a61ebf859c0571bcfb
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/26451
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

0 files changed, 0 insertions, 0 deletions