Add --disable-sbin-override for when /sbin is a symlink

mount.nfs* umount.nfs* and nfsdcltrack are currently always installed in
/sbin.

Many distros are moving to a "merged /usr" where /sbin and others are
symlinks into /usr/sbin or similar.  In these cases it is inelegant to
install in /sbin (i.e. install through a symlink).

So we add "--disable-sbin-override" as a configure option.  This causes
the same sbindir to be used for *mount.nfs* and nfsdcltrack as for other
system binaries.

Note that autotools notices if we simply define "sbindir=/sbin"
inside an "if CONFIG_foo" clause, gives a warning, and defeats our
intent.

So instead, we use the @CONFIG_SBIN_OVERRIDE_TRUE@ prefix to find
the new declaration when we don't want it.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Steve Dickson <steved@redhat.com>
diff --git a/configure.ac b/configure.ac
index bc2d0f0..93626d6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -187,6 +187,12 @@
 	enable_libmount=no
 fi
 
+AC_ARG_ENABLE(sbin-override,
+	[AC_HELP_STRING([--disable-sbin-override],
+		[Don't force nfsdcltrack and mount helpers into /sbin: always honour --sbindir])],
+	enable_sbin_override=$enableval,
+	enable_sbin_override=yes)
+	AM_CONDITIONAL(CONFIG_SBIN_OVERRIDE, [test "$enable_sbin_override" = "yes"])
 AC_ARG_ENABLE(junction,
 	[AC_HELP_STRING([--enable-junction],
 			[enable support for NFS junctions @<:@default=no@:>@])],
diff --git a/utils/mount/Makefile.am b/utils/mount/Makefile.am
index ad0be93..3101f7a 100644
--- a/utils/mount/Makefile.am
+++ b/utils/mount/Makefile.am
@@ -1,8 +1,10 @@
 ## Process this file with automake to produce Makefile.in
 
-# These binaries go in /sbin (not /usr/sbin), and that cannot be
-# overridden at config time.
-sbindir = /sbin
+# These binaries go in /sbin (not /usr/sbin), unless CONFIG_SBIN_OVERRIDE
+# is disabled as may be appropriate when /sbin is a symlink.
+# Note that we don't use "if CONFIG_SBIN_OVERRIDE" as that
+# causes autotools to notice the override and disable it.
+@CONFIG_SBIN_OVERRIDE_TRUE@sbindir = /sbin
 
 man8_MANS	= mount.nfs.man umount.nfs.man
 man5_MANS	= nfs.man
diff --git a/utils/nfsdcltrack/Makefile.am b/utils/nfsdcltrack/Makefile.am
index 2f7fe3d..769e4a4 100644
--- a/utils/nfsdcltrack/Makefile.am
+++ b/utils/nfsdcltrack/Makefile.am
@@ -1,8 +1,11 @@
 ## Process this file with automake to produce Makefile.in
 
-# These binaries go in /sbin (not /usr/sbin), and that cannot be
-# overridden at config time. The kernel "knows" the /sbin name.
-sbindir = /sbin
+# These binaries go in /sbin (not /usr/sbin) as the kernel "knows" the
+# /sbin name.  If /sbin is a symlink, CONFIG_SBIN_OVERRIDE can be
+# disabled to install in /usr/sbin anyway.
+# Note that we don't use "if CONFIG_SBIN_OVERRIDE" as that
+# causes autotools to notice the override and disable it.
+@CONFIG_SBIN_OVERRIDE_TRUE@sbindir = /sbin
 
 man8_MANS	= nfsdcltrack.man
 EXTRA_DIST	= $(man8_MANS)