memfd-test: move common code to a shared unit

The memfd & fuse tests will share more common code in the following
commits to test hugetlb support.

Link: http://lkml.kernel.org/r/20171107122800.25517-9-marcandre.lureau@redhat.com
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/memfd/common.h

@@ -0,0 +1,9 @@
+#ifndef COMMON_H_
+#define COMMON_H_
+
+extern int hugetlbfs_test;
+
+unsigned long default_huge_page_size(void);
+int sys_memfd_create(const char *name, unsigned int flags);
+
+#endif