[krbdev.mit.edu #5860] Build of windows/identity fails in clean directory

[Kevin Koch via RT]

krb5/src/windows/identity/copnfig/Makefile.w32 adds two directory 
levels between DESTROOT and DESTDIR.  Makefile does a mkdir of 
DESTROOT followed by a mkdir of DESTDIR.  For example,
mkdir ...\krb5\src\windows\identity\obj\ followed by 
mkdir ...\krb5\src\windows\identity\obj\i386\dbg

The second mkdir fails because i386 doesn't exist.  Adding an extra 
mkdir of $(DESTROOT)\$(CPU) fixes the problem.

Stylisticly, which is preferred:  adding another variable to 
Makefile.w32 and the new mkdir block in Makefile adds it, or the new 
mkdir block adds $(DESTROOT)\$(CPU)?