selftests/sgx: Include KHDR_INCLUDES in Makefile

Add KHDR_INCLUDES to the CFLAGS to pull in the kselftest harness
dependencies (-D_GNU_SOURCE).

Also, remove redefinitions of _GNU_SOURCE in the source code.

Fixes: 80921623 ("selftests/harness: remove use of LINE_MAX")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202404301040.3bea5782-oliver.sang@intel.comSigned-off-by: Edward Liaw <edliaw@google.com>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Tested-by: Jarkko Sakkinen <jarkko@kernel.org>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/sgx/Makefile

@@ -12,7 +12,7 @@ OBJCOPY := $(CROSS_COMPILE)objcopy
 endif
 
 INCLUDES := -I$(top_srcdir)/tools/include
-HOST_CFLAGS := -Wall -Werror -g $(INCLUDES) -fPIC
+HOST_CFLAGS := -Wall -Werror $(KHDR_INCLUDES) -g $(INCLUDES) -fPIC
 HOST_LDFLAGS := -z noexecstack -lcrypto
 ENCL_CFLAGS += -Wall -Werror -static-pie -nostdlib -ffreestanding -fPIE \
 	       -fno-stack-protector -mrdrnd $(INCLUDES)

tools/testing/selftests/sgx/sigstruct.c

 // SPDX-License-Identifier: GPL-2.0
 /*  Copyright(c) 2016-20 Intel Corporation. */
 
-#define _GNU_SOURCE
 #include <assert.h>
 #include <getopt.h>
 #include <stdbool.h>