rusticl: add a bunch of trivial tests

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35188>

src/gallium/frontends/rusticl/util/bitset.rs

@@ -7,3 +7,13 @@ pub fn test_bit(bitset: &[u32], bit: u32) -> bool {
 
     bitset[idx as usize] & (1 << test) != 0
 }
+
+#[test]
+fn test_test_bit() {
+    let data = [0x3254424d, 0xffffffff, 0x00000001];
+
+    assert!(test_bit(&data, 0));
+    assert!(!test_bit(&data, 5));
+    assert!(test_bit(&data, 64));
+    assert!(!test_bit(&data, 65));
+}

src/gallium/frontends/rusticl/util/math.rs

@@ -18,6 +18,13 @@ where
     b
 }
 
+#[test]
+fn gcd_test() {
+    assert_eq!(gcd(5, 15), 5);
+    assert_eq!(gcd(7, 15), 1);
+    assert_eq!(gcd(60, 45), 15);
+}
+
 pub struct SetBitIndices<T> {
     val: T,
 }