Use Option instead of String to make inling test pass

Contracts result in function calls that would make the inlining test
spuriously fail.

Author: tautschnig

tests/codegen-llvm/cross-crate-inlining/auxiliary/leaf.rs

@@ -4,8 +4,8 @@
 
 // This function *looks* like it contains a call, but that call will be optimized out by MIR
 // optimizations.
-pub fn leaf_fn() -> String {
-    String::new()
+pub fn leaf_fn() -> bool {
+    Some(0).is_some()
 }
 
 // This function contains a call, even after MIR optimizations. It is only eligible for

tests/codegen-llvm/cross-crate-inlining/leaf-inlining.rs

@@ -7,7 +7,7 @@ extern crate leaf;
 
 // Check that we inline a leaf cross-crate call
 #[no_mangle]
-pub fn leaf_outer() -> String {
+pub fn leaf_outer() -> bool {
     // CHECK-NOT: call {{.*}}leaf_fn
     leaf::leaf_fn()
 }