lib/gnat: Enable -Werror

We want to catch warnings as early as possible.

Change-Id: Ifdb2ff8f7973d557a437ac127e073306f76ca6f6
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33848
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/lib/gnat/Makefile.inc

@@ -25,6 +25,7 @@ ADAFLAGS_libgnat-$(1) := \
 	-gnatpg \
 	-I$$(src)/lib/gnat/ \
 	$$(GCC_ADAFLAGS_$(1)) \
+	-Werror \
 
 libgnat-$(1)-y += a-unccon.ads
 libgnat-$(1)-y += ada.ads