Piotr Caban (@piotr) commented about dlls/vccorlib140/Makefile.in:
MODULE = vccorlib140.dll IMPORTS = combase +PARENTSRC = ../msvcrt
I think it's better to not use `PARENTSRC` to share just one header. It's probably best to copy it for now. Another option is to move it to shared location but I'm not sure if it's generic enough (there are currently 2 copies of cxx.h and this patch will add 3rd).