posixmodule.c: osdefs.h inclusion should not depend on compiler

[TheShermanTanker]

osdefs.h should not be defined by the compiler used, this small patch moves an inclusion out of an _MSC_VER check into an MS_WINDOWS one to better honour the assumption that compiler and OS macros are independent

Linked PRs

• GH-95896: posixmodule.c: osdefs.h inclusion should not depend on compiler #95897
• [3.11] GH-95896: posixmodule.c: fix osdefs.h inclusion to not depend on compiler (GH-95897) #99788
• [3.10] GH-95896: posixmodule.c: fix osdefs.h inclusion to not depend on compiler (GH-95897) #99789

[kumaraditya303]

Thanks for the PR.