Auto-detect both if not set, and if GOARCH is not set use GOHOSTARCH.
GOHOSTARCH is used to set the -m32 or -m64 flags for gcc.
This is so that 64-bit can build binaries that run on 32-bit systems.
R=rsc, iant, brainman
CC=golang-dev
https://golang.org/cl/2342045
new script "quietgcc" installed in $HOME/bin during make.bash
runs gcc with warnings, turns off inappropriate ones,
greps out useless output.
quietgcc also makes sure to run the correct 64-bit gcc.
R=r
DELTA=38 (36 added, 0 deleted, 2 changed)
OCL=17493
CL=19599