The following compilation error occurs with an old version of glibc due to
a recent commit adding MADV_COLLAPSE testing:

 [root@localhost mm]# getconf GNU_LIBC_VERSION
 glibc 2.34
 [root@localhost mm]# make
   CC       hmm-tests
 hmm-tests.c: In function 'hmm_migrate_anon_huge_fault':
 hmm-tests.c:2355:27: error: 'MADV_COLLAPSE' undeclared (first use in this function); did you mean 'MADV_COLD'?
  2355 |  ret = madvise(map, size, MADV_COLLAPSE);
       |                           ^~~~~~~~~~~~~
       |                           MADV_COLD
 hmm-tests.c:2355:27: note: each undeclared identifier is reported only once for each function it appears in
 make: *** [../lib.mk:225: /root/code/linux/tools/testing/selftests/mm/hmm-tests] Error 1

Include linux/mman.h (which provides the definition of MADV_COLLAPSE) to
fix the build error.

Fixes: e3d8707358ea ("selftests/mm/hmm-tests: test pagemap reads of PMD device-private entries")
Signed-off-by: Zenghui Yu <zenghui.yu@linux.dev>
---
 tools/testing/selftests/mm/hmm-tests.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
index e4c49699f3f7..2f2b9879d100 100644
--- a/tools/testing/selftests/mm/hmm-tests.c
+++ b/tools/testing/selftests/mm/hmm-tests.c
@@ -23,6 +23,7 @@
 #include <time.h>
 #include <pthread.h>
 #include <limits.h>
+#include <linux/mman.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/mman.h>
-- 
2.53.0