[sil] Add support for UnsafeRawPointer to SILType and ASTSynthesis.

I am going to be using this type in some of the Builtins that I am adding. Just
chopping off part of the patch before I commit anything.

include/swift/AST/ASTSynthesis.h

@@ -52,13 +52,14 @@ enum SingletonTypeSynthesizer {
   _rawUnsafeContinuation,
   _void,
   _word,
-  _swiftInt,       // Swift.Int
-  _serialExecutor, // the '_Concurrency.SerialExecutor' protocol
-  _taskExecutor,   // the '_Concurrency.TaskExecutor' protocol
-  _actor,          // the '_Concurrency.Actor' protocol
-  _distributedActor,  // the 'Distributed.DistributedActor' protocol
+  _swiftInt,               // Swift.Int
+  _serialExecutor,         // the '_Concurrency.SerialExecutor' protocol
+  _taskExecutor,           // the '_Concurrency.TaskExecutor' protocol
+  _actor,                  // the '_Concurrency.Actor' protocol
+  _distributedActor,       // the 'Distributed.DistributedActor' protocol
   _unsafeRawBufferPointer, // UnsafeRawBufferPointer
-  _unconstrainedAny, // any ~Copyable & ~Escapable
+  _unconstrainedAny,       // any ~Copyable & ~Escapable
+  _unsafeRawPointer,       // UnsafeRawPointer
 };
 inline Type synthesizeType(SynthesisContext &SC,
                            SingletonTypeSynthesizer kind) {
@@ -93,6 +94,8 @@ inline Type synthesizeType(SynthesisContext &SC,
       ->getDeclaredInterfaceType();
   case _unsafeRawBufferPointer:
     return SC.Context.getUnsafeRawBufferPointerType();
+  case _unsafeRawPointer:
+    return SC.Context.getUnsafeRawPointerType();
   case _copyable:
     return SC.Context.getProtocol(KnownProtocolKind::Copyable)
         ->getDeclaredInterfaceType();

include/swift/SIL/SILType.h

@@ -1067,6 +1067,9 @@ public:
   /// Return Builtin.ImplicitActor.
   static SILType getBuiltinImplicitActorType(const ASTContext &ctx);
 
+  /// Return UnsafeRawPointer.
+  static SILType getUnsafeRawPointer(const ASTContext &ctx);
+
   //
   // Utilities for treating SILType as a pointer-like type.
   //

lib/SIL/IR/SILType.cpp

@@ -136,6 +136,11 @@ SILType SILType::getBuiltinImplicitActorType(const ASTContext &ctx) {
   return getPrimitiveObjectType(ctx.TheImplicitActorType->getCanonicalType());
 }
 
+SILType SILType::getUnsafeRawPointer(const ASTContext &ctx) {
+  return getPrimitiveObjectType(
+      ctx.getUnsafeRawPointerType()->getCanonicalType());
+}
+
 bool SILType::isTrivial(const SILFunction &F) const {
   auto contextType = hasTypeParameter() ? F.mapTypeIntoContext(*this) : *this;