Regression in rand crate

[brson]

See rust-random/rand#93

src/isaac.rs:134:37: 134:48 error: the type of this value must be known in this context
src/isaac.rs:134             ($x:expr) => ( self.mem[($x >> 2).0 as usize & (RAND_SIZE_USIZE - 1)] )
src/isaac.rs:373:42: 373:53 error: the type of this value must be known in this context
 src/isaac.rs:373                 *self.mem.get_unchecked((($x >> 3).0 as usize) & (RAND_SIZE_64 - 1))

[erickt]

Dup of #30713.