cmd/link/internal/ld: loop-variable aliasing in TestDeadcode

[bcmills]

2020-05-05T15:41:37-b4ecafc/plan9-arm
2020-05-05T05:13:26-9b18968/plan9-arm
2020-05-05T00:36:44-c9d5f60/plan9-arm
2020-05-04T17:40:00-a1ffbe9/plan9-arm

--- FAIL: TestDeadcode (0.00s)
    --- FAIL: TestDeadcode/reflectcall (4.47s)
        deadcode_test.go:42: [/boot/workdir/go/bin/go build -ldflags=-dumpdep -o /tmp/TestDeadcode160913525/typedesc.exe testdata/deadcode/typedesc.go]: exit status: 'go 42246: 1':
            # command-line-arguments
            _ -> _rt0_arm_plan9
            _rt0_arm_plan9 -> runtime.rt0_go
            _rt0_arm_plan9 -> _tos
            runtime.rt0_go -> runtime.emptyfunc
…
            type..eqfunc.[4]string -> type..eq.[4]string
            go build command-line-arguments: copying /tmp/go-build094893182/b001/exe/a.out to /tmp/TestDeadcode160913525/typedesc.exe: write /tmp/TestDeadcode160913525/typedesc.exe: file does not exist
FAIL
FAIL	cmd/link/internal/ld	4.628s

Looking at the related CL 231397, I notice the following fragment:

	for _, test := range tests {
		t.Run(test.src, func(t *testing.T) {
			t.Parallel()
			src := filepath.Join("testdata", "deadcode", test.src+".go")
			exe := filepath.Join(tmpdir, test.src+".exe")

The uses of test.src end up colliding, with the same file used in every subtest. (This is exactly the situation described in #35670.)

[gopherbot]

Change https://golang.org/cl/232377 mentions this issue: cmd/link: fix loop variable capturing in TestDeadcode