cmd/internal/testdir:0_10: Test/fixedbugs/issue15747.go failures

```
#!watchflakes
default <- pkg == "cmd/internal/testdir:0_10" && test == "Test/fixedbugs/issue15747.go"
```

Issue created automatically to collect these failures.

Example ([log](https://ci.chromium.org/b/8697283615237573537)):

=== RUN Test/fixedbugs/issue15747.go
=== PAUSE Test/fixedbugs/issue15747.go
=== CONT Test/fixedbugs/issue15747.go
testdir_test.go:1194: gc output:
/home/swarming/.swarming/w/ir/x/w/goroot/test/fixedbugs/issue15747.go:22: live at entry to f1: xx
/home/swarming/.swarming/w/ir/x/w/goroot/test/fixedbugs/issue15747.go:22: live at call to newobject: xx
/home/swarming/.swarming/w/ir/x/w/goroot/test/fixedbugs/issue15747.go:29: live at call to f2: &xx
/home/swarming/.swarming/w/ir/x/w/goroot/test/fixedbugs/issue15747.go:37: live at entry to f2: d
/home/swarming/.swarming/w/ir/x/w/goroot/test/fixedbugs/issue15747.go:39: live at call to newobject: d
testdir_test.go:147:
issue15747.go:22: no match for `live at call to mallocgcSmallScanNoHeaderSC[0-9]+: xx$` in:
issue15747.go:22: live at entry to f1: xx
issue15747.go:22: live at call to newobject: xx
issue15747.go:39: no match for `live at call to mallocgcSmallScanNoHeaderSC[0-9]+: d` in:
issue15747.go:39: live at call to newobject: d
Unmatched Errors:
issue15747.go:22: live at call to newobject: xx
issue15747.go:39: live at call to newobject: d

--- FAIL: Test/fixedbugs/issue15747.go (0.22s)

— [watchflakes](https://go.dev/wiki/Watchflakes)

Start with test/fixedbugs/issue15747.go and the failure-reporting code in testdir_test.go, then reproduce Test/fixedbugs/issue15747.go using the linked log as a reference. Determine whether the compiler output or the test's expected patterns are wrong; done means the test passes with diagnostics matching the intended behavior.

Written by the indexing model from the issue text.