tests/qtest: libqtest: Exclude the *_fds APIs for win32

tests/qtest: libqtest: Exclude the *_fds APIs for win32

libqmp.c::qmp_fd_vsend_fds() is not available on Windows, hence any
APIs in libqtest that call libqmp.c::qmp_fd_vsend_fds() should be
excluded for win32 too. This includes the following:

  * qtest_qmp_vsend_fds()
  * qtest_vqmp_fds()
  * qtest_qmp_fds()
  * qtest_qmp_add_client()

Note qtest_qmp_vsend() was wrongly written to call qmp_fd_vsend_fds()
previously, but it should call the non fds version API qmp_fd_vsend().

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20220925113032.1949844-35-bmeng.cn@gmail.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>