crossgcc/gnat.patch: Never treat warnings as errors

We used to disable individual warnings that are expected when building
our GCC version with a newer one. Not all warnings can be disabled
indvidually, though, and it's much easier to simply allow warnings.
As a plus, we get the warnings in the log (in case anybody would ever
look into it).

Partially fixes building with host GCC 12.1.

Change-Id: I8fafec4fc49db73b6dba311c775eea2cc92a9b48
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/64999
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

util/crossgcc/patches/gcc-11.2.0_gnat.patch

@@ -5,7 +5,7 @@
  
  # Extra flags to pass to recursive makes.
 -COMMON_ADAFLAGS= -gnatpg
-+COMMON_ADAFLAGS= -gnatpg -gnatwGUR
++COMMON_ADAFLAGS= -gnatpg -gnatwn
  ifeq ($(TREECHECKING),)
  CHECKING_ADAFLAGS=
  else