Revert "Makefile: Warn if flexible array members are not at the end"

This reverts commit f4acef92.

Reason for revert: '-Wflex-array-member-not-at-end' is new command
option came with GCC-14. older versions will not support it.

Change-Id: I179d0bc0db3e863645ae4c87e1534c5c20025dfb
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82758
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/Makefile.mk b/Makefile.mk
index 0358c88..e642ac7 100644
--- a/Makefile.mk
+++ b/Makefile.mk
@@ -501,7 +501,7 @@
 CFLAGS_common += -fstrict-aliasing -ffunction-sections -fdata-sections -fno-pie
 CFLAGS_common += -Wstring-compare
 ifeq ($(CONFIG_COMPILER_GCC),y)
-CFLAGS_common += -Wold-style-declaration -Wflex-array-member-not-at-end
+CFLAGS_common += -Wold-style-declaration
 # Don't add these GCC specific flags when running scan-build
 ifeq ($(CCC_ANALYZER_OUTPUT_FORMAT),)
 CFLAGS_common += -Wno-packed-not-aligned