[X86][MS-InlineAsm] Make the constraint *m to be simple place holder

D113096 solved the "undefined reference to xxx" issue by adding
constraint *m for the global var. But it has strong side effect due to
the symbol in the assembly being replaced with constraint variable.
This leads to some lowering fails. https://godbolt.org/z/h3nWoerPe

This patch fix the problem by use the constraint *m as place holder
rather than real constraint. It has negligible effect for the existing
code generation.

Reviewed By: skan

Differential Revision: https://reviews.llvm.org/D115225