cbfstool: Add `-Werror` to make all warnings into errors

Ensure that no changes with warnings are committed. Although using
`-Werror` is debatable [1][2].

[1] http://blog.flameeyes.eu/2009/02/future-proof-your-code-dont-use-werror
[2] http://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

Change-Id: I402f2d82dd4087d8a575b0a85305a02ef04bb537
Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-on: http://review.coreboot.org/2441
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>
1 file changed