add erf and erfc to nondet tests

Author: RalfJung

Diff for: tests/pass/float.rs

@@ -1424,6 +1424,8 @@ fn test_non_determinism() {
         ensure_nondet(|| 1.0f32.atan2(2.0f32));
         ensure_nondet(|| 0.5f32.atanh());
         ensure_nondet(|| 5.0f32.gamma());
+        ensure_nondet(|| 5.0f32.erf());
+        ensure_nondet(|| 5.0f32.erfc());
     }
     pub fn test_operations_f64(a: f64, b: f64) {
         test_operations_f!(a, b);
@@ -1446,6 +1448,8 @@ fn test_non_determinism() {
         ensure_nondet(|| 1.0f64.tanh());
         ensure_nondet(|| 0.5f64.atanh());
         ensure_nondet(|| 5.0f64.gamma());
+        ensure_nondet(|| 5.0f64.erf());
+        ensure_nondet(|| 5.0f64.erfc());
     }
     pub fn test_operations_f128(a: f128, b: f128) {
         test_operations_f!(a, b);