Add Bazel task to build on Intel Macs

This makes sure our toolchain works on hosts which are older Macs.

Previous mac builds had accidentally been working because they'd
run on machines which had previously run with recipes that
used the "install xcode" [1] step. This means when we start
running task drivers on Macs that only use the task driver (e.g.
the Intel macs I targeted for this new task), it would
fail with:

  Error in fail: Error Getting SDK path: xcode-select: note: No developer tools were found, requesting install.
  If developer tools are located at a non-default location on disk, use `sudo xcode-select --switch path/to/Xcode.app` to specify the Xcode that you wish to use for command line developer tools, and cancel the installation dialog.

This ports that command to our mac task drivers.

Unlike the task drivers, we don't use sudo to switch to the xcode,
instead we use DEVELOPER_DIR to achieve that.

I chose the MacBookPro15.1 machines (cpu:x86-64-i9-8950HK) because
we have the most of those. We have those on Mac 14 and 15 and I
don't really care which of those we run on (we are just compiling),
so I didn't specify.

[1] https://github.com/google/skia/blob/2c4e3993fd1c68ee7f1561a0fca782623ec6f1b0/infra/bots/recipe_modules/xcode/api.py#L56

Change-Id: I97bccf88498814554600ef0eb978a47ed8729971
Bug: 256863909
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1288656
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Kaylee Lubick <kjlubick@google.com>