cmd/compile: Bug in rewrite rules for AMD64 causes SHL instruction overflow and miscompilation [1.26 backport]

[gopherbot]

@Jorropo requested issue #79182 to be considered for backport to the next 1.26 minor release.

cc @gopherbot please open backport issues for 1.25 and 1.26

This is a misscompilation which was added in cd595be.

[Jorropo]

The needed backport is CL 774040 but I would advise to also backport CL 774041 as this is a safety check making sure this bug will never escape the compiler again, the safety check should never have any observable effects if the bug isn't present elsewhere.