buildgcc: Allow environment to override $CC/$CXX

Also check for the presence of the given commands or "gcc", "cc" in this
order if $CC is empty. To untangle the given compilers from boostrapped
ones, introduce hostcc() and hostcxx() functions that return the respec-
tive compilers to be used.

Change-Id: Ic947be53eec25331173ac82ed742017ca3fbf83c
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/20331
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
1 file changed