Auto merge of #49383 - nox:scalarpair, r=eddyb

Allow niche-filling dataful variants to be represented as a ScalarPair

r? @eddyb

src/test/codegen/function-arguments.rs

@@ -133,6 +133,12 @@ pub fn trait_borrow(_: &Drop) {
 pub fn trait_box(_: Box<Drop>) {
 }
 
+// CHECK: { i8*, i8* } @trait_option(i8* noalias %x.0, i8* %x.1)
+#[no_mangle]
+pub fn trait_option(x: Option<Box<Drop>>) -> Option<Box<Drop>> {
+  x
+}
+
 // CHECK: { [0 x i16]*, [[USIZE]] } @return_slice([0 x i16]* noalias nonnull readonly %x.0, [[USIZE]] %x.1)
 #[no_mangle]
 pub fn return_slice(x: &[u16]) -> &[u16] {