While we're building kernels -g (ie, makeoptions DEBUG=-g), use -O as it

provides truer debugger stack traces.  For those that want to stick with
-O2 kernel builds, one should probably add -fno-optimize-sibling-calls
so that each stack frame as a frame pointer.
It is semi-promissed by the Release Engineers that when RELENG_6 is
created we go back to -O2.

Desired by:	scottl, jhb

sys/conf/kern.pre.mk

@@ -22,7 +22,7 @@ COPTFLAGS?=-O
 . if ${MACHINE_ARCH} == "amd64"
 COPTFLAGS?=-O2 -frename-registers -pipe
 . else
-COPTFLAGS?=-O2 -pipe
+COPTFLAGS?=-O -pipe
 . endif
 . if ${COPTFLAGS:M-O[23s]} != ""
 COPTFLAGS+= -fno-strict-aliasing