[PATCH V2 10/10] selftests: vm: remove dependecy from internal kernel macros

[Muhammad Usama Anjum <usama.anjum@collabora.com>]

The defination of swap() is used from kernel's internal header when this
test is built in source tree. The build fails when this test is built
out of source tree as defination of swap() isn't found. Selftests
shouldn't depend on kernel's internal header files. They can only depend
on uapi header files. Add the defination of swap() to fix the build
error:

	gcc -Wall  -I/linux_mainline2/build/usr/include -no-pie    userfaultfd.c -lrt -lpthread -o /linux_mainline2/build/kselftest/vm/userfaultfd
	userfaultfd.c: In function ‘userfaultfd_stress’:
	userfaultfd.c:1530:3: warning: implicit declaration of function ‘swap’; did you mean ‘swab’? [-Wimplicit-function-declaration]
	 1530 |   swap(area_src, area_dst);
	      |   ^~~~
	      |   swab
	/usr/bin/ld: /tmp/cclUUH7V.o: in function `userfaultfd_stress':
	userfaultfd.c:(.text+0x4d64): undefined reference to `swap'
	/usr/bin/ld: userfaultfd.c:(.text+0x4d82): undefined reference to `swap'
	collect2: error: ld returned 1 exit status

Fixes: 2c769ed7137a ("tools/testing/selftests/vm/userfaultfd.c: use swap() to make code cleaner")
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
---
 tools/testing/selftests/vm/userfaultfd.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
index d3fd24f9fae8..d2480ab93037 100644
--- a/tools/testing/selftests/vm/userfaultfd.c
+++ b/tools/testing/selftests/vm/userfaultfd.c
@@ -119,6 +119,9 @@ struct uffd_stats {
 				 ~(unsigned long)(sizeof(unsigned long long) \
 						  -  1)))
 
+#define swap(a, b) \
+	do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
+
 const char *examples =
     "# Run anonymous memory test on 100MiB region with 99999 bounces:\n"
     "./userfaultfd anon 100 99999\n\n"
-- 
2.30.2