add clrex instruction

Reference: /n/atom/patch/applied/5cclrex
Date: Fri Feb  6 06:04:08 CET 2015
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/5c/5.out.h	Fri Feb  6 06:03:53 2015
+++ /sys/src/cmd/5c/5.out.h	Fri Feb  6 06:03:54 2015
@@ -156,6 +156,8 @@
 	ALDREXD,
 	ASTREXD,
 
+	ACLREX,
+
 	ALAST,
 };
 
--- /sys/src/cmd/5c/enam.c	Fri Feb  6 06:03:57 2015
+++ /sys/src/cmd/5c/enam.c	Fri Feb  6 06:03:58 2015
@@ -100,5 +100,6 @@
 	"STREX",
 	"LDREXD",
 	"STREXD",
+	"CLREX",
 	"LAST",
 };