Once DLLs and EXEs are built, they need to have their manifests
processed and signed. These steps are encapsulated in the EXEPREP and
DLLPREP Makefile macros. Use them instead of invoking each processing
macro individually.
In addition to building libasn1 as a DLL also add a build target
so that a list of exports can be generated and used to check with
the .def file whether any exports are being left out.
Be explicit about dependencies. A subsequent invocation of the NTMakefile
should correctly deduce dependencies for generated files instead of
assuming they are always out of date.
