selftests: tdx: Use installed kernel headers search path

Use $(KHDR_INCLUDES) as lookup path for installed kernel headers rather
than using kernel headers in include/uapi from the source kernel tree
kernel headers.
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>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/tdx/Makefile

 # SPDX-License-Identifier: GPL-2.0
 
-CFLAGS += -O3 -Wl,-no-as-needed -Wall -static
+CFLAGS += -O3 -Wl,-no-as-needed -Wall $(KHDR_INCLUDES) -static
 
 TEST_GEN_PROGS := tdx_guest_test
 

tools/testing/selftests/tdx/tdx_guest_test.c

@@ -12,8 +12,8 @@
 #include <errno.h>
 #include <fcntl.h>
 
+#include <linux/tdx-guest.h>
 #include "../kselftest_harness.h"
-#include "../../../../include/uapi/linux/tdx-guest.h"
 
 #define TDX_GUEST_DEVNAME "/dev/tdx_guest"
 #define HEX_DUMP_SIZE 8