go: os: (*Process).Wait sometimes hangs on netbsd

greplogs --dashboard -md -l -e 'panic: test timed out.*\n\n(?:goroutine .*:\n(?:.+\n\t.+\n)+\n)*goroutine \d+ \[syscall, \d+ minutes\]:\n(?:.+\n\t.+\n)*os\.\(\*Process\)\.Wait(?:.*\n)+FAIL\s+cmd/link'

2021-12-12T06:14:07-9c6e8f6/netbsd-386-9_0-n2

goroutine 29 [syscall, 2 minutes]:
syscall.Syscall6(0x21a8, 0x892ee8c, 0x0, 0x8a2c1e0, 0x0, 0x0, 0x0)
	/tmp/workdir/go/src/syscall/asm_unix_386.s:43 +0x5 fp=0x892ee38 sp=0x892ee34 pc=0x80b9605
syscall.wait4(0x21a8, 0x892ee8c, 0x0, 0x8a2c1e0)
	/tmp/workdir/go/src/syscall/zsyscall_netbsd_386.go:34 +0x5b fp=0x892ee70 sp=0x892ee38 pc=0x80b737b
syscall.Wait4(0x21a8, 0x892eeb0, 0x0, 0x8a2c1e0)
	/tmp/workdir/go/src/syscall/syscall_bsd.go:144 +0x3b fp=0x892ee94 sp=0x892ee70 pc=0x80b558b
os.(*Process).wait(0x8a04660)
	/tmp/workdir/go/src/os/exec_unix.go:43 +0x82 fp=0x892eec8 sp=0x892ee94 pc=0x80de982
os.(*Process).Wait(...)
	/tmp/workdir/go/src/os/exec.go:132
os/exec.(*Cmd).Wait(0x8a18fd0)
	/tmp/workdir/go/src/os/exec/exec.go:507 +0x4d fp=0x892ef0c sp=0x892eec8 pc=0x816b07d
os/exec.(*Cmd).Run(0x8a18fd0)
	/tmp/workdir/go/src/os/exec/exec.go:341 +0x43 fp=0x892ef1c sp=0x892ef0c pc=0x816a463
os/exec.(*Cmd).CombinedOutput(0x8a18fd0)
	/tmp/workdir/go/src/os/exec/exec.go:567 +0x89 fp=0x892ef30 sp=0x892ef1c pc=0x816b549
cmd/link.TestContentAddressableSymbols(0x89290e0)
	/tmp/workdir/go/src/cmd/link/link_test.go:879 +0x136 fp=0x892ef9c sp=0x892ef30 pc=0x83824b6
testing.tRunner(0x89290e0, 0x842c054)
	/tmp/workdir/go/src/testing/testing.go:1410 +0x10d fp=0x892efe4 sp=0x892ef9c pc=0x813d19d
testing.(*T).Run.func1()
	/tmp/workdir/go/src/testing/testing.go:1457 +0x28 fp=0x892eff0 sp=0x892efe4 pc=0x813df78
runtime.goexit()
	/tmp/workdir/go/src/runtime/asm_386.s:1311 +0x1 fp=0x892eff4 sp=0x892eff0 pc=0x80ab211
created by testing.(*T).Run
	/tmp/workdir/go/src/testing/testing.go:1457 +0x36e

2021-10-29T18:34:24-903f313/netbsd-amd64-9_0 2021-10-01T15:59:38-e5ad363/netbsd-arm-bsiegert

goroutine 28 [syscall, 27 minutes]:
syscall.Syscall6(0x1c1, 0xd1f, 0xa09db4, 0x0, 0x9b27e0, 0x0, 0x0)
	/var/gobuilder/buildlet/go/src/syscall/asm_netbsd_arm.s:39 +0x8 fp=0xa09d5c sp=0xa09d58 pc=0x8d3f8
syscall.wait4(0xd1f, 0xa09db4, 0x0, 0x9b27e0)
	/var/gobuilder/buildlet/go/src/syscall/zsyscall_netbsd_arm.go:35 +0x54 fp=0xa09d94 sp=0xa09d5c pc=0x8a694
syscall.Wait4(0xd1f, 0xa09dd8, 0x0, 0x9b27e0)
	/var/gobuilder/buildlet/go/src/syscall/syscall_bsd.go:145 +0x3c fp=0xa09db8 sp=0xa09d94 pc=0x88c58
os.(*Process).wait(0x983290)
	/var/gobuilder/buildlet/go/src/os/exec_unix.go:44 +0x100 fp=0xa09df0 sp=0xa09db8 pc=0xb4f1c
os.(*Process).Wait(...)
	/var/gobuilder/buildlet/go/src/os/exec.go:132
os/exec.(*Cmd).Wait(0x98cc60)
	/var/gobuilder/buildlet/go/src/os/exec/exec.go:507 +0x50 fp=0xa09e2c sp=0xa09df0 pc=0x1482d0
os/exec.(*Cmd).Run(0x98cc60)
	/var/gobuilder/buildlet/go/src/os/exec/exec.go:341 +0x48 fp=0xa09e3c sp=0xa09e2c pc=0x147810
os/exec.(*Cmd).CombinedOutput(0x98cc60)
	/var/gobuilder/buildlet/go/src/os/exec/exec.go:567 +0x98 fp=0xa09e50 sp=0xa09e3c pc=0x14882c
cmd/link.TestIssue33979.func2({0x983200, 0x21}, {0x9ea0a0, 0x9, 0x9})
	/var/gobuilder/buildlet/go/src/cmd/link/link_test.go:199 +0x90 fp=0xa09ea8 sp=0xa09e50 pc=0x368e14
cmd/link.TestIssue33979.func3({0x9ea0a0, 0x9, 0x9})
	/var/gobuilder/buildlet/go/src/cmd/link/link_test.go:206 +0x60 fp=0xa09ecc sp=0xa09ea8 pc=0x368d5c
cmd/link.TestIssue33979(0x8834a0)
	/var/gobuilder/buildlet/go/src/cmd/link/link_test.go:239 +0x3bc fp=0xa09f98 sp=0xa09ecc pc=0x368790
testing.tRunner(0x8834a0, 0x41871c)
	/var/gobuilder/buildlet/go/src/testing/testing.go:1389 +0x118 fp=0xa09fe0 sp=0xa09f98 pc=0x1195d4
testing.(*T).Run.func1()
	/var/gobuilder/buildlet/go/src/testing/testing.go:1436 +0x30 fp=0xa09fec sp=0xa09fe0 pc=0x11a448
runtime.goexit()
	/var/gobuilder/buildlet/go/src/runtime/asm_arm.s:824 +0x4 fp=0xa09fec sp=0xa09fec pc=0x7d028
created by testing.(*T).Run
	/var/gobuilder/buildlet/go/src/testing/testing.go:1436 +0x3a0

2021-09-21T20:39:31-48cf96c/netbsd-arm-bsiegert 2021-09-14T14:27:57-181e8cd/netbsd-arm-bsiegert 2021-04-29T15:47:16-12eaefe/freebsd-amd64-11_4 2021-04-28T13:49:52-4fe324d/netbsd-386-9_0 2021-03-05T02:30:31-b62da08/netbsd-386-9_0 2021-02-19T00:40:05-95a44d2/netbsd-arm64-bsiegert 2019-09-04T21:52:18-aae0b5b/linux-ppc64le-power9osu

#44801 may be closely related.

Note that many of this failures are on architectures not believed to be affected by #49209.

@bsiegert, @coypoop: any ideas?