cmake,win32*.sh: Windows DLL support

cmake,win32*.sh: Windows DLL support

At the moment, the Windows binaries can only be linked statically.
This is less than ideal since:

* the resulting binaries can be quite large, especially when
including debug symbols
* librados and librbd cannot be used directly by 3rd party apps
* the build duration is increased

In order to do a dynamic build, we'll:

* add an option to win32_build.sh
* fix link order
* dynamically link boost
* disable the "-pie" flag when using Mingw, which generates incorrect
  executable entry points
* by default, cmake generates import libs for executables. The issue
  is that for rados.exe, it generates librados.dll.a, thus overriding
  the librados.dll import library, which breaks the build process.
  We'll configure cmake to skip generating import libs for executables.

Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>