[llvm-lib] Pass the right value of MingwDef to parseCOFFModuleDefinition

In llvm-lib cases, the MinGW specific behaviours shouldn't be
enabled.

Not adding any tests to check the corner case behaviours, as this
simply was a mistake when this codepath was added in
395ec445 / D144765.

Differential Revision: https://reviews.llvm.org/D152362