runtime: use HOST_CC to compile mkversion
runtime: use HOST_CC to compile mkversion

HOST_CC is set in Make.inc, so use that rather
than hardcoding quietgcc

R=golang-dev, iant
CC=golang-dev
http://codereview.appspot.com/4515163

Committer: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

dsriram/golang,tv42/old-go,gnanderson/go,gnanderson/go,apparentlymart/golang,gnanderson/go,dsriram/golang,gnanderson/go,dsriram/golang,apparentlymart/golang,tv42/old-go,tv42/old-go,tv42/old-go,ssrl/go,gnanderson/go,ssrl/go,gnanderson/go,ssrl/go,tv42/old-go,pombredanne/go-deleteme,ssrl/go,pombredanne/go-deleteme,dsriram/golang,pombredanne/go-deleteme,dsriram/golang,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,ssrl/go,apparentlymart/golang,dsriram/golang,dsriram/golang,apparentlymart/golang,gnanderson/go,ssrl/go,tv42/old-go,pombredanne/go-deleteme,ssrl/go,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme