CP command used in the phobos windows makefile

[Andrej Mitrovic]

Well that doesn't work:

D:\DMD\dmd2\src\phobos>make install -fwin32.mak
cp phobos.lib \dmd2\windows\lib
C:\GnuWin32\bin\cp.exe: cannot create regular file
`\\dmd2\\windows\\lib': No such file or directory

Having DIR defined as:
DIR=\dmd2

as a directory doesn't make sense either. I have a feeling make
install is either never used or whoever packs windows binaries
(Walter?) calls it via cygwin or some other shell. Or there's a CP
binary that I don't know about.

I'll just roll out a build script in D for myself so I can have some
way of quickly building and switching between branches. I'll make it
multithreaded to speed things up as well.