cbfstool: Bump C version to C11

cbfstool depends on vboot headers, and vboot expects to be able to use
modern C features like _Static_assert(). It just so happens that it
doesn't do that in any headers included from cbfstool right now, but
that may change. Let's switch cbfstool to a newer version to prevent
that from becoming a problem.

Change-Id: I884e1bdf4ec21487ddb1bca57ef5dc2104cf8e0e
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37666
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

util/cbfstool/Makefile.inc

@@ -129,10 +129,10 @@ ifeq ($(shell uname -s | cut -c-7 2>/dev/null), MINGW32)
 TOOLCFLAGS += -mno-ms-bitfields
 endif
 ifeq ($(shell uname -o 2>/dev/null), Cygwin)
-TOOLCFLAGS+=-std=gnu99
+TOOLCFLAGS+=-std=gnu11
 TOOLCPPFLAGS+=-D_GNU_SOURCE
 else
-TOOLCFLAGS+=-std=c99
+TOOLCFLAGS+=-std=c11
 endif
 
 $(objutil)/cbfstool/%.o: $(objutil)/cbfstool/%.c