fix interpreter in watchman python binaries
fix interpreter in watchman python binaries

Summary:
watchman-diag (any also watchman-make) error with an interpreter error when run with out a python interpreter specified:

```
watchman-diag
zsh: /opt/facebook/bin/watchman-diag: bad interpreter: /usr/local/fbprojects/packages/xcode/227/xcode_14.0.0_14A309.app/Contents/Developer/usr/bin/python3: no such file or directory
```

We have fixed this a couple times before:
- D29084022 (https://github.com/facebook/watchman/commit/b52a2782759c05e54da9e79c15add0b4dd832ac3)
- D33344805 (https://github.com/facebook/watchman/commit/84c1bf622967f1ed4cbceded09480f6e5ba245cd)

The issue here is that the default python at `/usr/bin/python3` points to a path on sandcastle that does not exist locally. We want to use the `/usr/local/bin/python3` which has the same path on sandcastle as locally (its the platform python symlink).

Recently, our python shebangs broke because they started pointing at  `/usr/bin/python3` instead of `/usr/local/bin/python3`.

I believe the reason is as follows:

By default when cmake searches for a python, it favors the most recent python version, even if that version is not the one hinted at with the `Python3_ROOT_DIR` setting. i.e. if cmake finds two pythons with the same version it will pick the one hinted at by `Python3_ROOT_DIR`, but if it finds two pythons with different versions it will pick the latest one no matter what and ignore the `Python3_ROOT_DIR` hint.

see https://gitlab.kitware.com/cmake/cmake/-/issues/21186 for a complaint of this.

on Sandcastle macs `/usr/bin/python3` has been updated father than  `/usr/local/bin/python3`. I'm guessing this happened about 3 weeks ago when we started to get complaints of this, but I haven't confirmed yet.

```
[root@mactest2717.02.prn6 ~]# /usr/local/bin/python3 --version
Python 3.8.9
[root@mactest2717.02.prn6 ~]# /usr/bin/python3 --version
Python 3.9.6
```

We can change cmake's version priority to a location priority, so that cmake will prefer the pythons it finds in `Python3_ROOT_DIR`.

Admittedly, this isn't a great solution, but it will patch up things for now. Rice's changes to move to a rust `watchmanctl rage` will make this issue less apparent since only the non diag python scripts can be effected by this type of bug, and if we migrate our watchman builds to buck, buck will manage our python things much better for us.

Reviewed By: fanzeyi

Differential Revision: D40030619

fbshipit-source-id: 6a4fe687e418e63f64bd26818025ba63365527b7

facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman