patches: make re-applied patches idempotent (#26784)

We use POSIX `patch` to apply patches to files when building, but
`patch` by default prompts the user when it looks like a patch
has already been applied. This means that:

1. If a patch lands in upstream and we don't disable it
   in a package, the build will start failing.
2. `spack develop` builds (which keep the stage around) will
   fail the second time you try to use them.

To avoid that, we can run `patch` with `-N` (also called
`--forward`, but the long option is not in POSIX). `-N` causes
`patch` to just ignore patches that have already been applied.
This *almost* makes `patch` idempotent, except that it returns 1
when it detects already applied patches with `-N`, so we have to
look at the output of the command to see if it's safe to ignore
the error.

- [x] Remove non-POSIX `-s` option from `patch` call
- [x] Add `-N` option to `patch`
- [x] Ignore error status when `patch` returns 1 due to `-N`
- [x] Add tests for applying a patch twice and applying a bad patch
- [x] Tweak `spack.util.executable` so that it saves the error that
      *would have been* raised with `fail_on_error=True`. This lets
      us easily re-raise it.

Co-authored-by: Greg Becker <becker33@llnl.gov>

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