Integration test file-based race condition

[davidlattimore]

I just saw the following failure in CI. It succeeded when rerun.

---- integration_test::program_name_32___gnu_unique_c__ stdout ----
Error: Failed to build program `gnu-unique.c` with linker `wild` config `default`
  Caused by:
    libwild reported error. Rerun command(s):
 cargo run --bin wild -- -static --gc-sections -z now -o /__w/wild/wild/wild/tests/build/gnu-unique.c-default-host.wild /__w/wild/wild/wild/tests/build/gnu-unique.default-host-4be4ca568d55e803.o /__w/wild/wild/wild/tests/build/runtime.default-host-aa1bc7c9f5809698.o /__w/wild/wild/wild/tests/build/gnu-unique-1.default-host-1ddb3af3d24ec04c.o /__w/wild/wild/wild/tests/build/gnu-unique-2.default-host-977a00c48193e385.o --validate-output --write-layout --write-trace
    The file `/__w/wild/wild/wild/tests/build/runtime.default-host-aa1bc7c9f5809698.o` was changed while we were running

Ideally each file should only be written once when running. This might also explain an issue observed with using nextest with the Nix CI changes.

[davidlattimore]

I've got no idea how this happens. I've run the tests under strace after deleting wild/tests/build and there were three runtime.default-host-*.o files, but each was only written once. We create and flock a lock file while the file is being created.

[marxin]

One more example of the issue: https://github.com/davidlattimore/wild/actions/runs/15804675983/job/44547771013?pr=912