Fix some `i128` shift-related bugs in x64 backend.#2682

Merged

cfallin merged 2 commits intobytecodealliance:mainfrom cfallin:shift-bugs

Feb 26, 2021

+144-316

Commits on Feb 23, 2021

Fix some i128 shift-related bugs in x64 backend.
cfallin
committed

Commits on Feb 25, 2021

Fix 128-bit left shift: null out tmp3, not tmp2, on zero-shift case.
cfallin
committed