selftests: arm64: Fix incorrect kernel headers search path

Use $(KHDR_INCLUDES) as lookup path for kernel headers. This prevents
building against kernel headers from the build environment in scenarios
where kernel headers are installed into a specific output directory
(O=...).
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
Cc: Ingo Molnar <mingo@redhat.com>
Cc: <stable@vger.kernel.org>  # 5.18+
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/arm64/fp/Makefile

@@ -3,7 +3,7 @@
 # A proper top_srcdir is needed by KSFT(lib.mk)
 top_srcdir = $(realpath ../../../../../)
 
-CFLAGS += -I$(top_srcdir)/usr/include/
+CFLAGS += $(KHDR_INCLUDES)
 
 TEST_GEN_PROGS := fp-stress \
 	sve-ptrace sve-probe-vls \

tools/testing/selftests/arm64/tags/Makefile

 # SPDX-License-Identifier: GPL-2.0
 
-CFLAGS += -I../../../../../usr/include/
+CFLAGS += $(KHDR_INCLUDES)
 TEST_GEN_PROGS := tags_test
 TEST_PROGS := run_tags_test.sh