https://issues.dlang.org/show_bug.cgi?id=23224

          Issue ID: 23224
           Summary: ImportC: memory model switch is not passed to C
                    preprocessor
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: bugzilla@digitalmars.com

I.e. -m32 or -m64

--