Rollup merge of #40832 - pftbest:fix_msp430, r=stjepang

libcore: fix compilation on 16bit target (MSP430).

Since PR #40601 has been merged, libcore no longer compiles on MSP430.
The reason is this code in `break_patterns`:
```rust
 let mut random = len;
 random ^= random << 13;
 random ^= random >> 17;
 random ^= random << 5;
 random &= modulus - 1;
```
It assumes that `len` is at least a 32 bit integer.
As a workaround replace `break_patterns` with an empty function for 16bit targets.

cc @stjepang
cc @alexcrichton