Require Type::Equal() for all type equality comparisons.

Previously, we uniqued AtomicTypes, so that they could be compared
by pointer equality, but with forthcoming SOA variability changes,
this would become too unwieldy (lacking a more general / ubiquitous
type uniquing implementation.)

func.cpp

@@ -355,7 +355,7 @@ Function::emitCode(FunctionEmitContext *ctx, llvm::Function *function,
         // issue a warning.  Also need to warn if it's the entry block for
         // the function (in which case it will not have predeccesors but is
         // still reachable.)
-        if (type->GetReturnType() != AtomicType::Void &&
+        if (Type::Equal(type->GetReturnType(), AtomicType::Void) == false &&
             (pred_begin(ec.bblock) != pred_end(ec.bblock) || (ec.bblock == entryBBlock)))
             Warning(sym->pos, "Missing return statement in function returning \"%s\".",
                     type->rType->GetString().c_str());