kselftest/arm64: signal: drop now redundant GNU_SOURCE definition

The definition of GNU_SOURCE was recently centralised in an upper layer
kselftest Makefile, so the definition in the arm64 signal tests Makefile
is no longer needed. To make things worse, since both definitions are
not strictly identical, the compiler warns about it:
<command-line>: warning: "_GNU_SOURCE" redefined
<command-line>: note: this is the location of the previous definition

Drop the definition in the arm64/signal Makefile.

Fixes: cc937da ("selftests: centralize -D_GNU_SOURCE= to CFLAGS in lib.mk")
Signed-off-by: Andre Przywara <[email protected]>
Reviewed-by: Mark Brown <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>

Author: Andre-ARM

tools/testing/selftests/arm64/signal/Makefile

@@ -2,7 +2,7 @@
 # Copyright (C) 2019 ARM Limited
 
 # Additional include paths needed by kselftest.h and local headers
-CFLAGS += -D_GNU_SOURCE -std=gnu99 -I.
+CFLAGS += -std=gnu99 -I.
 
 SRCS := $(filter-out testcases/testcases.c,$(wildcard testcases/*.c))
 PROGS := $(patsubst %.c,%,$(SRCS))