Get the alignment correct for subclasses of AvailabilitySpec.

Apart from being required by the standard, we also store these objects
in a PointerIntPair, so it's important to not misalign them.

(We should have an -fsanitize=undefined bot to catch this.)

Author: jrose-apple

include/swift/AST/AvailabilitySpec.h

@@ -89,6 +89,12 @@ class VersionConstraintAvailabilitySpec : public AvailabilitySpec {
   static bool classof(const AvailabilitySpec *Spec) {
     return Spec->getKind() == AvailabilitySpecKind::VersionConstraint;
   }
+
+  void *
+  operator new(size_t Bytes, ASTContext &C,
+               unsigned Alignment = alignof(VersionConstraintAvailabilitySpec)){
+    return AvailabilitySpec::operator new(Bytes, C, Alignment);
+  }
 };
 
 /// A wildcard availability specification that guards execution
@@ -115,6 +121,12 @@ class OtherPlatformAvailabilitySpec : public AvailabilitySpec {
   static bool classof(const AvailabilitySpec *Spec) {
     return Spec->getKind() == AvailabilitySpecKind::OtherPlatform;
   }
+
+  void *
+  operator new(size_t Bytes, ASTContext &C,
+               unsigned Alignment = alignof(OtherPlatformAvailabilitySpec)) {
+    return AvailabilitySpec::operator new(Bytes, C, Alignment);
+  }
 };
 
 } // end namespace swift