Allow call_intrin to call an LLVM intrinsic with void return type. (h…

…alide#7048)

Have ```CodeGen_LLVM::get_vector_type``` return the void type if passed the void type as a scalar base. This makes it possible to call intrinsics returning void via ```CodeGenn_LLVM::call_intrin```.

Should be very safe as currently this anything doing this would fail inside the routine. The change breaks the invariant that any thing returned from get_vector_type is a vector type, but propagating void for function return types is a pretty standard behavior and if this was not intended, it will very likely fail just outside this instead of having failed inside the use. I.e. very low chance of spurious errors from this.

src/CodeGen_LLVM.cpp

@@ -4528,7 +4528,9 @@ Value *CodeGen_LLVM::call_intrin(const llvm::Type *result_type, int intrin_lanes
                                  llvm::Function *intrin, vector<Value *> arg_values) {
     internal_assert(intrin);
     int arg_lanes = 1;
-    if (result_type->isVectorTy()) {
+    if (result_type->isVoidTy()) {
+        arg_lanes = intrin_lanes;
+    } else if (result_type->isVectorTy()) {
         arg_lanes = get_vector_num_elements(result_type);
     }
 
@@ -4913,6 +4915,10 @@ llvm::Type *CodeGen_LLVM::get_vector_type(llvm::Type *t, int n,
                                           VectorTypeConstraint type_constraint) const {
     bool scalable;
 
+    if (t->isVoidTy()) {
+        return t;
+    }
+
     switch (type_constraint) {
     case VectorTypeConstraint::None:
         scalable = effective_vscale != 0 &&