Replace stddef.h by string.h in win32 platform specifics
Replace stddef.h by string.h in win32 platform specifics

For some reasons, <corecrt.h> fails to compile on my machine, but <stddef.h> fails on the C.I.
The stack of uncompatible macros is getting really fragile...
This commit is only a wild guess.
IMO we should try and follow standards where possible.

OpenSmalltalk/vm,OpenSmalltalk/vm,timfel/squeakvm,timfel/squeakvm,OpenSmalltalk/vm,OpenSmalltalk/vm,timfel/squeakvm,timfel/squeakvm,timfel/squeakvm,timfel/squeakvm,OpenSmalltalk/vm,OpenSmalltalk/vm,timfel/squeakvm,OpenSmalltalk/vm,OpenSmalltalk/vm,timfel/squeakvm