libdm: pkgconfig: fix devmapper.pc to not reference nonexistent rt.pc file

librt doesn't have a pkgconfig file so use Libs.private: -lrt instead
to declare the dependency directly.

The same applies for -lm which is also used and which hasn't been
defined in the devmapper.pc file yet.

WHATS_NEW_DM

@@ -1,5 +1,6 @@
 Version 1.02.107 - 
 ===================================
+  Fix devmapper.pc pkgconfig file to not reference non-existent rt.pc file.
   Reinstate dm_task_get_info@Base to libdevmapper exports. (1.02.106)
 
 Version 1.02.106 - 26th August 2015

configure

@@ -659,7 +659,7 @@ SELINUX_PC
 SELINUX_LIBS
 REPLICATORS
 READLINE_LIBS
-RT_PC
+RT_LIB
 RAID
 PYTHON_LIBDIRS
 PYTHON_INCDIRS
@@ -12847,7 +12847,7 @@ fi
 $as_echo "#define HAVE_REALTIME 1" >>confdefs.h
 
 		LIBS="-lrt $LIBS"
-		RT_PC="librt"
+		RT_LIB="-lrt"
 	else
 		{ $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: Disabling realtime clock" >&5
 $as_echo "$as_me: WARNING: Disabling realtime clock" >&2;}

configure.in

@@ -1581,7 +1581,7 @@ if test "$REALTIME" = yes; then
 	if test "$HAVE_REALTIME" = yes; then
 		AC_DEFINE([HAVE_REALTIME], 1, [Define to 1 to include support for realtime clock.])
 		LIBS="-lrt $LIBS"
-		RT_PC="librt"
+		RT_LIB="-lrt"
 	else
 		AC_MSG_WARN(Disabling realtime clock)
 	fi
@@ -1995,7 +1995,7 @@ AC_SUBST(PYTHON_LIBDIRS)
 AC_SUBST(QUORUM_CFLAGS)
 AC_SUBST(QUORUM_LIBS)
 AC_SUBST(RAID)
-AC_SUBST(RT_PC)
+AC_SUBST(RT_LIB)
 AC_SUBST(READLINE_LIBS)
 AC_SUBST(REPLICATORS)
 AC_SUBST(SACKPT_CFLAGS)

libdm/libdevmapper.pc.in

@@ -8,4 +8,5 @@ Description: device-mapper library
 Version: @DM_LIB_PATCHLEVEL@
 Cflags: -I${includedir} 
 Libs: -L${libdir} -ldevmapper
-Requires.private: @SELINUX_PC@ @UDEV_PC@ @RT_PC@
+Requires.private: @SELINUX_PC@ @UDEV_PC@
+Libs.private: -lm @RT_LIB@