Convert to clamav's build system -> impl. cross-compilation support (tblgen)

Right now static linking of libclamav doesn't work with llvm parts for a number
of reasons:
1. llvm is not built with libtool, and it builds .a files (or .so files)
2. if I link with .a files, that works for a .so (LLVM's .a files are PIC), but
 the created libclamav.a will miss the .a files, so I'd need to install the llvm
 .a files together with clamav's
3. libtool solves this by putting individual .o files into the target libtool .a
archive, but since I link against non-libtool archives it doesn't know how to do
that
4. if I link against a .so then obviously it is not static linking

If llvm would be converted to clamav's buildsystem then static linking of
libclamav would work.