Add linkage to libm when compositor is used (bug #6231)

configure.ac.in

@@ -164,6 +164,7 @@ dnl Xcomposite and related extensions
 dnl
 compositor="no"
 ENABLE_COMPOSITOR=""
+MATH_LIBS=""
 AC_ARG_ENABLE([compositor],
 AC_HELP_STRING([--enable-compositor], [enable compositor in xfwm4 (default)])
 AC_HELP_STRING([--disable-compositor], [disable compositor in xfwm4]),
@@ -175,10 +176,14 @@ if test x"$enable_compositor" = x"yes"; then
       PKG_CHECK_MODULES(COMPOSITOR, xcomposite >= [xcomposite_minimum_version] xfixes xdamage)
       AC_DEFINE([HAVE_COMPOSITOR], [1], [Define to enable compositor])
       ENABLE_COMPOSITOR="--enable-compositor"
+      AC_DEFINE([HAVE_COMPOSITOR], [1], [Define to enable compositor])
       compositor="yes"
+      dnl Math lib is required for compositor internals
+      MATH_LIBS=" -lm"
     fi
   fi
 fi
+AC_SUBST([MATH_LIBS])
 AC_SUBST(ENABLE_COMPOSITOR)
 
 dnl

src/Makefile.am

@@ -107,7 +107,8 @@ xfwm4_LDADD =								\
 	$(LIBSTARTUP_NOTIFICATION_LIBS)					\
 	$(RENDER_LIBS)							\
 	$(COMPOSITOR_LIBS)						\
-	$(RANDR_LIBS)
+	$(RANDR_LIBS) 							\
+	$(MATH_LIBS)	
 
 EXTRA_DIST = 								\
 	inline-default-icon.h default_icon.png default_icon.svg		\