move include of sys/mount back to where it was

Turns out the sys/mount.h can be tricky to use
because various other system include files sometimes redefine
some of the symbols in this include file, leading
to compile failures.

Careful ordering of include files may solve the problem,
but here it simpler just to move the include of sys/mount.h
back to its original location.

related to #12181

Signed-off-by: Howard Pritchard <howardp@lanl.gov>

Author: hppritcha

ompi/mca/fs/base/base.h

@@ -43,9 +43,6 @@
 #ifdef HAVE_SYS_PARAM_H
 #include <sys/param.h>
 #endif
-#ifdef HAVE_SYS_MOUNT_H
-#include <sys/mount.h>
-#endif
 #ifdef HAVE_SYS_STAT_H
 #include <sys/stat.h>
 #endif

ompi/mca/fs/base/fs_base_get_parent_dir.c

@@ -35,6 +35,14 @@
 #include "ompi/mca/fs/base/base.h"
 #include "ompi/mca/common/ompio/common_ompio.h"
 
+/*
+ * Be careful moving this include.
+ * It's easy to hit problems similar to that reported in
+ * https://github.com/systemd/systemd/issues/8507
+ */
+#ifdef HAVE_SYS_MOUNT_H
+#include <sys/mount.h>
+#endif
 
 void mca_fs_base_get_parent_dir ( char *filename, char **dirnamep)
 {