Add C rules for builtin mul overflow

In C++, builtin mul overflow is a variadic function: `bool (...)`. In C
is an unprototyped function: `int ()`.

Author: lucic71

rules/builtin/tgt_refcount.rs

@@ -13,3 +13,13 @@ fn f10(a0: i64, a1: i64, a2: Ptr<i64>) -> bool {
     a2.write(val);
     ovf
 }
+fn f12(a0: i64, a1: i64, a2: Ptr<i64>) -> bool {
+    let (val, ovf) = a0.overflowing_mul(a1);
+    a2.write(val);
+    ovf
+}
+fn f13(a0: i64, a1: i64, a2: Ptr<i64>) -> bool {
+    let (val, ovf) = a0.overflowing_mul(a1);
+    a2.write(val);
+    ovf
+}

rules/builtin/tgt_unsafe.rs

@@ -38,4 +38,14 @@ unsafe fn f10(a0: i64, a1: i64, a2: *mut i64) -> bool {
 #[cfg(any(target_arch = "x86_64", target_arch = "x86"))]
 unsafe fn f11() {
     std::hint::spin_loop();
+
+unsafe fn f12(a0: i64, a1: i64, a2: *mut i64) -> bool {
+    let (val, ovf) = a0.overflowing_mul(a1);
+    *a2 = val;
+    ovf
+}
+unsafe fn f13(a0: i64, a1: i64, a2: *mut i64) -> bool {
+    let (val, ovf) = a0.overflowing_mul(a1);
+    *a2 = val;
+    ovf
 }