add macOS 12/SDK version check (M1 fix)

[thejasonfisher]

Build was breaking on 12.x or with the new Xcode --

• Incorporated a change to use brew to get the openssl path
• Added tests for 12.x with a fallback to 10.9 deploy target (must match openssl deploy target)
• Added tests for new MacOS.sdk location with fallback to old
• Built and tested with: export B_BUILD_TYPE=Release ./clean_build.sh
• Self-signed with: codesign --force --deep --sign - /Applications/Barrier.app

This shouldn't change anything user-facing, i.e. break compatibility with older versions, but I have not tested that yet. This works on my M1 MacBook Air as a native Apple Silicon app.

Contributor Checklist:

• I have created a file in the doc/newsfragments directory IF it is a
  user-visible change (and make sure to read the README.md in that directory)

[thejasonfisher]

All tests passed? There is no longer a Mojava test available.

[feiyax]

Data point: this build works for me on my MBP16 with M1 Pro, running osx 12.2.1

[dlobue]

FYI this didn't work for me. I kept getting errors about the linker not finding -lSystem until I made the following change:

-    OSX_SYSROOT="$(xcode-select --print-path)/SDKs/MacOSX.platform/Developer/SDKs/MacOSX.sdk"
+    OSX_SYSROOT="$(xcode-select --print-path)/SDKs/MacOSX.sdk"

[jgworks]

Works great on MacBook Pro (16-inch, 2021) macOS Monterey 12.5.1 (21G83)