runtime: stack allocate Panic structure during runtime.panic
runtime: stack allocate Panic structure during runtime.panic

Update issue 7347

When runtime.panic is called the *Panic is malloced from the heap. This can lead to a gc cycle while panicing which can make a bad situation worse.

It appears to be possible to stack allocate the Panic and avoid malloc'ing during a panic.

Ref: https://groups.google.com/d/topic/golang-dev/OfxqpklGkh0/discussion

LGTM=minux.ma, dvyukov, rsc
R=r, minux.ma, gobot, rsc, dvyukov
CC=golang-codereviews
https://codereview.appspot.com/66830043

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang