macOS SDK upgraded to 11.0

[Greg Tatum]

If you are specifying a 10.12 or lower version of the macOS SDK in your mozconfig you will most likely get build errors. e.g.

'Vision/Vision.h' file not found
#import <Vision/Vision.h>
        ^~~~~~~~~~~~~~~~~
1 error generated.

The fix is to either remove SDK line from your mozconfig (which will use the SDK from your xcode) or upgrade to at least version 10.13.

SDK upgrade:

https://bugzilla.mozilla.org/show_bug.cgi?id=1696504

macOS Text recognition APIs (requires 10.13 to build)

https://bugzilla.mozilla.org/show_bug.cgi?id=1759504

~Greg Tatum

[Stephen A Pohl]

A change has been queued on autoland to require the macOS 11 (or higher)
SDK to build Firefox on macOS. The documentation to build Firefox will
be updated simultaneously:
https://bugzilla.mozilla.org/show_bug.cgi?id=1696513.

This brings the requirements for local builds in line with what is
already happening on CI (see
https://bugzilla.mozilla.org/show_bug.cgi?id=1696504).

This change allowed us to remove many workarounds that were in place to
enable building with older SDKs:
https://bugzilla.mozilla.org/show_bug.cgi?id=1773752.