Only check if compass is available through sass if sass was found.

configure.ac

@@ -94,16 +94,18 @@ if test x"${COMPASS}" == x"" ; then
 fi
 AC_SUBST(COMPASS)
 
-AC_MSG_CHECKING([for compass support in sass])
-tempfile=`mktemp`
-$SASS --compass $tempfile > /dev/null 2> /dev/null
-sass_compass=$?
-rm $tempfile
-if test x"${sass_compass}" != x"0" ; then
-    AC_MSG_RESULT([not available])
-    AC_MSG_WARN([Please install compass so it can be used using "sass --compass ...".])
+if test x"${SASS}" != x"" ; then
+    AC_MSG_CHECKING([for compass support in sass])
+    tempfile=`mktemp`
+    $SASS --compass $tempfile > /dev/null 2> /dev/null
+    sass_compass=$?
+    rm $tempfile
+    if test x"${sass_compass}" != x"0" ; then
+        AC_MSG_RESULT([not available])
+        AC_MSG_WARN([Please install compass so it can be used using "sass --compass ...".])
+    fi
+    AC_MSG_RESULT([ok])
 fi
-AC_MSG_RESULT([ok])
 
 AC_PATH_PROGS([AUTOPREFIXER],[autoprefixer])
 if test x"${AUTOPREFIXER}" == x"" ; then