[Darwin] Fix Objective-C NeXT ABI version check diagnostics.

[Darwin] Fix Objective-C NeXT ABI version check diagnostics.

This fixes build errors when used with newer GCC and corrects a mistake
in the checking of ABI versions.

276768 We were missing a check for the case that user's ABI was > 2 and the
codegen was for 64 bit.

276635 Fix some format-related build warnings.

This fixes two error messages to avoid punctuation and contracted
negations.

2019-10-30  Iain Sandoe  <iain@sandoe.co.uk>

	Backport from mainline
	2019-10-09  Iain Sandoe  <iain@sandoe.co.uk>

	* config/darwin.c (darwin_override_options): Make the check for
	Objective-C ABI version more specific for 64bit code.

	Backport from mainline
	2019-10-06  Iain Sandoe  <iain@sandoe.co.uk>

	* config/darwin.c (darwin_override_options): Adjust objective-c
	ABI version error messages to avoid punctuation and contracted
	negations.

From-SVN: r277645