Add regression test for https://bugs.swift.org/browse/SR-4571

Author: slavapestov

validation-test/compiler_crashers_2_fixed/sr-4571.swift

@@ -0,0 +1,16 @@
+// RUN: %target-swift-frontend -emit-ir %s
+
+func add(_ a: Int, _ b: Int) throws -> Int {
+    return a + b
+}
+
+func add(_ a: Int, _ b: Int) -> Float {
+    return Float(a + b)
+}
+
+func useAdd() {
+    guard let c: Float = try? add(3, 4) else {
+        return
+    }
+    print(c)
+}