WHPX: dynamically load WHP libraries

WHPX: dynamically load WHP libraries

We're currently linking against import libraries of the WHP DLLs.

By dynamically loading the libraries, we ensure that QEMU will work
on previous Windows versions, where the WHP DLLs will be missing
(assuming that WHP is not requested).

Also, we're simplifying the build process, as we no longer require
the import libraries.

Signed-off-by: Alessandro Pilotti <apilotti@cloudbasesolutions.com>
Signed-off-by: Justin Terry (VM) <juterry@microsoft.com>
Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>
Message-Id: <1526405722-10887-2-git-send-email-lpetrut@cloudbasesolutions.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>