mem.zeroes .Array improvements

Before (when given an array with many elements):
```
zig\std\mem.zig:345:13: error: evaluation exceeded 1000
backwards branches
            for (array) |*element| {
            ^
```
related to https://github.com/ziglang/zig/issues/4847#issuecomment-605721461
ef419dd72dSebastian committed on 3/30/2020, 3:16:25 PM· committed by Andrew Kelleyparent3be720a
1 file changedLine totals unavailable