[clang] [llvm] [AArch64] set AppleA14 architecture version to v8.4-a (PR #92600)

[Ahmed Bougacha via llvm-commits]

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@@ -718,12 +718,16 @@ def ProcessorFeatures {
   list<SubtargetFeature> AppleA13 = [HasV8_4aOps, FeatureCrypto, FeatureFPARMv8,
                                      FeatureNEON, FeaturePerfMon, FeatureFullFP16,
                                      FeatureFP16FML, FeatureSHA3];
+  // Apple A14 and M1 chips are based on Armv8.5-a but without BTI. Since there
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ahmedbougacha wrote:

I don't think we need to emphasize this here or in `aarch64-target-features.c`;  it's just v8.4a with some bits from .5, and there are other instances of that.  This wasn't always explained clearly in the ARM ARM extension list, but the more recent issues make this pattern explicit (e.g., looking at DDI 0487K.a: A2.1.1, or the start of A2.2.5)

https://github.com/llvm/llvm-project/pull/92600