Fix:

gcc: error: unrecognized command-line option ‘-Wflex-array-member-not-at-end’

by making the compiler option dependent on its support.

Fixes: 1838731f1072c ("selftest: af_unix: Add -Wall and -Wflex-array-member-not-at-end to CFLAGS.")
Cc: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
v2: Just using cc-option is insufficient since it is not defined,
    and if it is not defined it just disables the option entirely.
    Include Makefile.compiler and declare the function locally
    to solve the problem.

 tools/testing/selftests/net/af_unix/Makefile | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/net/af_unix/Makefile b/tools/testing/selftests/net/af_unix/Makefile
index 3cd677b72072..4c0375e28bbe 100644
--- a/tools/testing/selftests/net/af_unix/Makefile
+++ b/tools/testing/selftests/net/af_unix/Makefile
@@ -1,4 +1,9 @@
-CFLAGS += $(KHDR_INCLUDES) -Wall -Wflex-array-member-not-at-end
+top_srcdir := ../../../../..
+include $(top_srcdir)/scripts/Makefile.compiler
+
+cc-option = $(call __cc-option, $(CC),,$(1),$(2))
+
+CFLAGS += $(KHDR_INCLUDES) -Wall $(call cc-option,-Wflex-array-member-not-at-end)
 
 TEST_GEN_PROGS := \
 	diag_uid \
-- 
2.45.2