[Sema] Migrate away from PointerUnion::{is,get} (NFC)

Note that PointerUnion::{is,get} have been soft deprecated in
PointerUnion.h:

  // FIXME: Replace the uses of is(), get() and dyn_cast() with
  //        isa<T>, cast<T> and the llvm::dyn_cast<T>

I'm moving the definitions of several functions to SemaConcept.cpp
because llvm::cast requires the full definitions of
NormalizedConstraintPair, which is used like so:

  using CompoundConstraint = llvm::PointerIntPair<NormalizedConstraintPair *, 1,
                                                  CompoundConstraintKind>;

Author: kazutakahirata

clang/include/clang/Sema/SemaConcept.h

@@ -135,31 +135,20 @@ struct NormalizedConstraint {
     return *this;
   }
 
-  bool isAtomic() const { return Constraint.is<AtomicConstraint *>(); }
+  bool isAtomic() const { return llvm::isa<AtomicConstraint *>(Constraint); }
   bool isFoldExpanded() const {
-    return Constraint.is<FoldExpandedConstraint *>();
+    return llvm::isa<FoldExpandedConstraint *>(Constraint);
   }
-  bool isCompound() const { return Constraint.is<CompoundConstraint>(); }
+  bool isCompound() const { return llvm::isa<CompoundConstraint>(Constraint); }
 
-  CompoundConstraintKind getCompoundKind() const {
-    assert(isCompound() && "getCompoundKind on a non-compound constraint..");
-    return Constraint.get<CompoundConstraint>().getInt();
-  }
+  CompoundConstraintKind getCompoundKind() const;
 
   NormalizedConstraint &getLHS() const;
   NormalizedConstraint &getRHS() const;
 
-  AtomicConstraint *getAtomicConstraint() const {
-    assert(isAtomic() &&
-           "getAtomicConstraint called on non-atomic constraint.");
-    return Constraint.get<AtomicConstraint *>();
-  }
+  AtomicConstraint *getAtomicConstraint() const;
 
-  FoldExpandedConstraint *getFoldExpandedConstraint() const {
-    assert(isFoldExpanded() &&
-           "getFoldExpandedConstraint called on non-fold-expanded constraint.");
-    return Constraint.get<FoldExpandedConstraint *>();
-  }
+  FoldExpandedConstraint *getFoldExpandedConstraint() const;
 
 private:
   static std::optional<NormalizedConstraint>

clang/lib/Sema/SemaConcept.cpp

@@ -1958,3 +1958,21 @@ concepts::TypeRequirement::TypeRequirement(TypeSourceInfo *T) :
     Value(T),
     Status(T->getType()->isInstantiationDependentType() ? SS_Dependent
                                                         : SS_Satisfied) {}
+
+NormalizedConstraint::CompoundConstraintKind
+NormalizedConstraint::getCompoundKind() const {
+  assert(isCompound() && "getCompoundKind on a non-compound constraint..");
+  return cast<CompoundConstraint>(Constraint).getInt();
+}
+
+AtomicConstraint *NormalizedConstraint::getAtomicConstraint() const {
+  assert(isAtomic() && "getAtomicConstraint called on non-atomic constraint.");
+  return cast<AtomicConstraint *>(Constraint);
+}
+
+FoldExpandedConstraint *
+NormalizedConstraint::getFoldExpandedConstraint() const {
+  assert(isFoldExpanded() &&
+         "getFoldExpandedConstraint called on non-fold-expanded constraint.");
+  return cast<FoldExpandedConstraint *>(Constraint);
+}