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
Constraint `*m` should be used when the address of a variable is passed
as a value. And the constraint is missing for MS inline assembly when sth
is written to the address of the variable.
The missing would cause FE delete the definition of the static varible,
and then result in "undefined reference to xxx" issue.
Reviewed By: xiangzhangllvm
Differential Revision: https://reviews.llvm.org/D113096
