This fixes `.INVAL => unreachable` being triggered by the cache system
on macOS when multiple processes race to create the same compilation.
The problem is that when two processes race to create a file, it
sometimes returns ENOENT even though that error code is nonsensical for
this situation.
Commit 2b0929929d purportedly solved this,
but it did not open the file with write permissions, leading to the
EINVAL panic later on. This commit remedies the situation by introducing
a loop and simply retrying when the ENOENT occurs.
There are no dir components, so you would think that this was
unreachable, however we have observed on macOS two processes racing
to do openat() with O_CREAT manifest in ENOENT.
Now that this API is used by the build system, these debug logs are
problematic because build scripts run in debug mode, making these logs
noisy output.
Andrew Kelley