The windows builders are failing with a message about leftover panic in traceback,
evidence of a bug in CL 100870044. 

The bug is not windows-specific; windows was just lucky enough to trigger it somewhat
reliably. This variant of the program crashing on windows crashes everywhere.

g% cat x.go
package main

import "runtime"

func main() {
    func() {
        defer func() {
            runtime.GC()
            recover()
        }()
        var x [8192]byte
        func(x [8192]byte) {
            defer func() {
                if err := recover(); err != nil {
                    panic("wrap: " + err.(string))
                }
            }()
            panic("bad")
        }(x)
    }()
}
g% go run x.go
runtime: g16: leftover panic argp=0x2080a3f08 pc=0x2170
fatal error: traceback has leftover defers or panics

runtime stack:
runtime.throw(0x52ff7)
    /Users/rsc/g/go/src/pkg/runtime/panic.c:520 +0x69 fp=0x7fff5fbff2b8 sp=0x7fff5fbff2a0
runtime.gentraceback(0xab36, 0x2208245f48, 0x0, 0x20807c120, 0x0, 0x0, 0x7fffffff,
0x9270, 0x7fff5fbff4a0, 0x0)
    /Users/rsc/g/go/src/pkg/runtime/traceback_x86.c:312 +0x3a3 fp=0x7fff5fbff3a0 sp=0x7fff5fbff2b8
addstackroots(0x20807c120, 0x7fff5fbff4a0)
    /Users/rsc/g/go/src/pkg/runtime/mgc0.c:1692 +0x168 fp=0x7fff5fbff430 sp=0x7fff5fbff3a0
markroot(0x208090480, 0x5)
    /Users/rsc/g/go/src/pkg/runtime/mgc0.c:1321 +0xbe fp=0x7fff5fbff4b0 sp=0x7fff5fbff430
runtime.parfordo(0x208090480)
    /Users/rsc/g/go/src/pkg/runtime/parfor.c:88 +0xa3 fp=0x7fff5fbff528 sp=0x7fff5fbff4b0
gc(0x2208245f60)
    /Users/rsc/g/go/src/pkg/runtime/mgc0.c:2407 +0x1d6 fp=0x7fff5fbff658 sp=0x7fff5fbff528
mgc(0x20807c120)
    /Users/rsc/g/go/src/pkg/runtime/mgc0.c:2349 +0x2e fp=0x7fff5fbff668 sp=0x7fff5fbff658
runtime.mcall(0x20957)
    /Users/rsc/g/go/src/pkg/runtime/asm_amd64.s:181 +0x4b fp=0x7fff5fbff678 sp=0x7fff5fbff668

goroutine 16 [garbage collection]:
runtime.gc(0x2)
    /Users/rsc/g/go/src/pkg/runtime/mgc0.c:2329 +0x1c6 fp=0x2208245f78 sp=0x2208245f48
runtime.GC()
    /Users/rsc/g/go/src/pkg/runtime/malloc.goc:853 +0x26 fp=0x2208245f88 sp=0x2208245f78
main.func·001()
    /Users/rsc/winshare/x.go:8 +0x1e fp=0x2208245fa8 sp=0x2208245f88
----- stack segment boundary -----
runtime.panic(0x272c0, 0x20807a030)
    /Users/rsc/g/go/src/pkg/runtime/panic.c:248 +0x18d fp=0x2208247f50 sp=0x2208247eb8
main.func·002()
    /Users/rsc/winshare/x.go:15 +0xce fp=0x2208247fa8 sp=0x2208247f50
----- stack segment boundary -----
runtime.panic(0x272c0, 0x20807a010)
    /Users/rsc/g/go/src/pkg/runtime/panic.c:248 +0x18d fp=0x2080a3f08 sp=0x2080a3e70
main.func·003(0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
    /Users/rsc/winshare/x.go:18 +0x7f fp=0x2080a3f40 sp=0x2080a3f08
main.func·004()
    /Users/rsc/winshare/x.go:19 +0x94 fp=0x2080a7f48 sp=0x2080a3f40
main.main()
    /Users/rsc/winshare/x.go:20 +0x1a fp=0x2080a7f50 sp=0x2080a7f48
runtime.main()
    /Users/rsc/g/go/src/pkg/runtime/proc.c:247 +0x11a fp=0x2080a7fa8 sp=0x2080a7f50
runtime.goexit()
    /Users/rsc/g/go/src/pkg/runtime/proc.c:1445 fp=0x2080a7fb0 sp=0x2080a7fa8
created by _rt0_go
    /Users/rsc/g/go/src/pkg/runtime/asm_amd64.s:97 +0x120

goroutine 17 [runnable]:
runtime.MHeap_Scavenger()
    /Users/rsc/g/go/src/pkg/runtime/mheap.c:507 fp=0x2208249fa8 sp=0x2208249fa0
runtime.goexit()
    /Users/rsc/g/go/src/pkg/runtime/proc.c:1445 fp=0x2208249fb0 sp=0x2208249fa8
created by runtime.main
    /Users/rsc/g/go/src/pkg/runtime/proc.c:207

goroutine 18 [runnable]:
bgsweep()
    /Users/rsc/g/go/src/pkg/runtime/mgc0.c:1976 fp=0x220822dfa8 sp=0x220822dfa0
runtime.goexit()
    /Users/rsc/g/go/src/pkg/runtime/proc.c:1445 fp=0x220822dfb0 sp=0x220822dfa8
created by runtime.gc
    /Users/rsc/g/go/src/pkg/runtime/mgc0.c:2268
exit status 2
g%