Use a magic value other than 42

Shifting a literal (which is an int when a suffix is not present)
generates a warning because the only possible result is 0, and the
programmer probably didn't intend to do that.

Change the shift to a value less than 32. The test exhibiting the
warning wasn't aiming to test integer promotion rules, so I've opted
to change the constant.

tests/rust/prefix.rs

@@ -1,7 +1,7 @@
-pub const LEN: i32 = 42;
+pub const LEN: i32 = 22;
 
 pub type NamedLenArray = [i32; LEN];
-pub type ValuedLenArray = [i32; 42];
+pub type ValuedLenArray = [i32; 22];
 
 #[repr(u8)]
 pub enum AbsoluteFontWeight {
@@ -14,7 +14,7 @@ pub enum AbsoluteFontWeight {
 pub extern "C" fn root(x: NamedLenArray, y: ValuedLenArray, z: AbsoluteFontWeight) { }
 
 #[no_mangle]
-pub const X: i64 = 42 << 42;
+pub const X: i64 = 22 << 22;
 
 #[no_mangle]
 pub const Y: i64 = X + X;