[gen] use ext wildcard in forbidden file

Author: Shale Xiong

gen/libdir/forbidden.conf

@@ -64,7 +64,7 @@
 # let Exp-obs =
 #   [Exp & M]; rf & ext; [Exp & M]
 #   | [Exp & M]; ca & ext; [Exp & M]
--safe Rfe Fre Coe
+-safe Ext
 
 #let Exp-haz-ob = [Exp & R]; (po & same-loc); [Exp & R]; (ca & ext); [Exp & W]
 -safe [PosRR Fre]