Back out gcc workaround per re@ request. Details:

"There seems to be some continuing discussion about how this is best fixed,
and we'd like to get Alexander (as our gcc guru) to opine on a final
solution before picking one.  In the mean time, could you back out the
original commit (sys.mk:1.89)?"

Approved by:	re (rwatson)

share/mk/sys.mk

@@ -35,7 +35,7 @@ CC		?=	c89
 CFLAGS		?=	-O
 .else
 CC		?=	cc
-CFLAGS		?=	-O2 -fno-strict-aliasing -fno-tree-vrp -pipe
+CFLAGS		?=	-O2 -fno-strict-aliasing -pipe
 .endif
 
 CXX		?=	c++