mm/selftests: fix pagemap_ioctl memory map test

__FILE__ is not guaranteed to exist in current dir.  Replace that with
argv[0] for memory map test.

Link: https://lkml.kernel.org/r/20231116201547.536857-4-peterx@redhat.com
Fixes: 46fd75d ("selftests: mm: add pagemap ioctl tests")
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: xzpeter

tools/testing/selftests/mm/pagemap_ioctl.c

@@ -36,6 +36,7 @@ int pagemap_fd;
 int uffd;
 int page_size;
 int hpage_size;
+const char *progname;
 
 #define LEN(region)	((region.end - region.start)/page_size)
 
@@ -1149,11 +1150,11 @@ int sanity_tests(void)
 	munmap(mem, mem_size);
 
 	/* 9. Memory mapped file */
-	fd = open(__FILE__, O_RDONLY);
+	fd = open(progname, O_RDONLY);
 	if (fd < 0)
 		ksft_exit_fail_msg("%s Memory mapped file\n", __func__);
 
-	ret = stat(__FILE__, &sbuf);
+	ret = stat(progname, &sbuf);
 	if (ret < 0)
 		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
 
@@ -1472,12 +1473,14 @@ static void transact_test(int page_size)
 			      extra_thread_faults);
 }
 
-int main(void)
+int main(int argc, char *argv[])
 {
 	int mem_size, shmid, buf_size, fd, i, ret;
 	char *mem, *map, *fmem;
 	struct stat sbuf;
 
+	progname = argv[0];
+
 	ksft_print_header();
 
 	if (init_uffd())