Add -Werror to xcompile's testcc

If -Werror is not specified, tests for certain compiler flags
will emit a warning, which makes the build break since we compile
with -Werror.

Change-Id: I7be56530ff9f94e5500bad226c83e47145a808d7
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/336
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>
1 file changed