[InstCombine] Add optimization to prevent poison from being propagated.

In D104569, Freeze was inserted just before br to solve the `branching on undef` miscompilation problem.
But value analysis was being disturbed by added freeze.

```
v = load ptr
cond = freeze(icmp (and v, const), const')
br cond, ...
```
The case in which value analysis disturbed is as above.
By changing freeze to add immediately after load, value analysis will be successful again.

```
v = load ptr
freeze(icmp (and v, const), const')
=>
v = load ptr
v' = freeze v
icmp (and v', const), const'
```
In this patch, I propose the above optimization.
With this patch, the poison will not spread as the freeze is performed early.

Reviewed By: nikic, lebedev.ri

Differential Revision: https://reviews.llvm.org/D105392