[llvm] [clang] [AArch64] Make +pauth enabled in Armv8.3-a by default (PR #78027)

[Anatoly Trosinenko via cfe-commits]

atrosinenko wrote:

Ping.

A few notes:
* not setting `__ARM_FEATURE_PAUTH` in `getTargetDefinesARMV83A()` anymore (and thus relying on conditionally setting it in `getTargetDefines()`) makes the existing tests check that `HasPAuth` is set if v8.3+ architecture extension is requested
* in the Pointer Authentication section of `aarch64-target-features.c` test, one more test case is added (for the "negative" case `armv8.5-a+nopauth` that is supported now), other changes are to account for FEAT_PAUTH support and pac-ret being separate options and all four combinations are possible

https://github.com/llvm/llvm-project/pull/78027