The Interix Software Development Kit (SDK) contains X11R5
libraries, header files, and various other tools specifically for
building X Window utilities.
Several of the tools provided as part of the Interix SDK (cpp(1),
imake(1),
xmkmf(1),
mkdirhier(1), and makedepend(1)) are necessary to build X11 software
packages provided by third parties. In particular, the cpp
implementation, found in /usr/contrib/bin/cpp, is intended
only for use by imake, not by the C compiler.
,
imake(1)