HasPAuth should be implicitly set by Armv8.3, I think

There are several features that are mandatory in some Armv8.x-A
extensions but they are not set in AArch64TargetInfo::setArchFeatures().

Author: atrosinenko

clang/lib/Basic/Targets/AArch64.cpp

@@ -90,6 +90,7 @@ void AArch64TargetInfo::setArchFeatures() {
       HasFlagM = true;
     }
     if (ArchInfo->Version.getMinor() >= 3u) {
+      HasPAuth = true;
       HasRCPC = true;
       FPU |= NeonMode;
     }
@@ -121,6 +122,7 @@ void AArch64TargetInfo::setArchFeatures() {
     HasDotProd = true;
     HasDIT = true;
     HasFlagM = true;
+    HasPAuth = true;
     HasRCPC = true;
     FPU |= NeonMode;
     HasCCPP = true;