cmd/go/internal/lockedfile: use a retry loop to suppress EDEADLK on AIX and Solaris

AIX, Solaris, and Illumos all appear to implement fcntl deadlock
detection at the granularity of processes. However, we are acquiring
and releasing file locks on individual goroutines running
concurrently: our locking occurs at a much finer granularity. As a
result, these platforms occasionally fail with EDEADLK errors, when
they detect locks that would be _misordered_ in a single-threaded
program but are safely _unordered_ in a multi-threaded context.

To work around the spurious errors, we treat EDEADLK as always
spurious, and retry the failing system call with a bounded exponential
backoff. This approach may introduce substantial latency since we no
longer benefit from kernel-scheduled wakeups in case of collisions,
but high-latency operations seem better than spurious failures.

Updates #33974
Updates #35618
Fixes #32817

Change-Id: I58b2c6a0f143bce55d6460fd4ddc3db83577ada7
Reviewed-on: https://go-review.googlesource.com/c/go/+/222277


Reviewed-by: Jay Conrod <jayconrod@google.com>