Strip versioning components from *HOST for Darwin and Solaris

--- a/aclocal.m4
+++ b/aclocal.m4
@@ -1358,6 +1358,12 @@
   freebsd*)
     $2="freebsd"
     ;;
+  darwin*)
+    $2="darwin"
+	;;
+  solaris2.*)
+    $2="solaris2"
+	;;
   *)
     echo "Unknown OS $1"
     exit 1