add some configure options to control external libtextcat and libtextcat data

libtextcat/makefile.mk

@@ -30,6 +30,12 @@ PRJ=.
 PRJNAME=libtextcat
 TARGET=libtextcat
 
+.IF "$(SYSTEM_LIBTEXTCAT)" == "YES"
+all:
+    @echo "An already available installation of libtextcat should exist on your system."
+    @echo "Therefore the version provided here does not need to be built in addition."
+.ENDIF
+
 # --- Settings -----------------------------------------------------
 
 .INCLUDE :	settings.mk