[WebAssembly] Fix scheduling dependencies in register-stackified code

[WebAssembly] Fix scheduling dependencies in register-stackified code

Add physical register defs to instructions used from stackified
instructions to prevent them from being scheduled into the middle of
a stack sequence. This is a conservative measure which may be loosened
in the future.

Differential Revision: http://reviews.llvm.org/D15252

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254811 91177308-0d34-0410-b5e6-96231b3b80d8