runtime: TestSmhasherWindowed is still flaky on linux-386-longtest

[bcmills]

2020-12-10T22:58:49-6d3d3fb/linux-386-longtest

##### GOMAXPROCS=2 runtime -cpu=1,2,4 -quick
--- FAIL: TestSmhasherWindowed (27.87s)
    hash_test.go:566: 32 bit keys
    hash_test.go:161: unexpected number of collisions: got=512 mean=0.499992 stddev=0.707101 threshold=156.565200
    hash_test.go:568: 64 bit keys
    hash_test.go:570: string keys
--- FAIL: TestSmhasherWindowed (26.69s)
    hash_test.go:566: 32 bit keys
    hash_test.go:161: unexpected number of collisions: got=512 mean=0.499992 stddev=0.707101 threshold=156.565200
    hash_test.go:568: 64 bit keys
    hash_test.go:570: string keys
--- FAIL: TestSmhasherWindowed (26.69s)
    hash_test.go:566: 32 bit keys
    hash_test.go:161: unexpected number of collisions: got=512 mean=0.499992 stddev=0.707101 threshold=156.565200
    hash_test.go:568: 64 bit keys
    hash_test.go:570: string keys
FAIL
FAIL	runtime	598.996s

2020-10-26T21:47:49-36c5edd/linux-386-longtest

--- FAIL: TestSmhasherWindowed (26.23s)
    hash_test.go:566: 32 bit keys
    hash_test.go:161: unexpected number of collisions: got=512 mean=0.499992 stddev=0.707101 threshold=156.565200
    hash_test.go:568: 64 bit keys
    hash_test.go:161: unexpected number of collisions: got=512 mean=0.499992 stddev=0.707101 threshold=156.565200
    hash_test.go:570: string keys
FAIL
FAIL	runtime	169.624s

See previously #39352.

I would guess that it's flaky on 32-bit ARM too, but we don't have a longtest builder for that configuration.

CC @randall77