win32_build.sh: use ENABLE_SHARED=ON by default

win32_build.sh: use ENABLE_SHARED=ON by default

The Windows build script uses static linking by default, the
reason being that some tests were failing to build otherwise,
mostly due to unspecified dependencies.

Now that the issue was addressed, we can enable dynamic linking
by default.

Worth mentioning that the Ceph MSI build script already uses
dynamic linking.

While at it, we'll drop some duplicate defaults from
"win32_deps_build.sh". For better clarity, we'll avoid exporting
some "win32_build.sh" variables, instead passing them explicitly
to "win32_deps_build.sh".

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