Remove BUILD_TESTS=OFF in configuring LibXml2 on windows.
Remove BUILD_TESTS=OFF in configuring LibXml2 on windows.

hsorby/libcellml,nickerso/libcellml,hsorby/libcellml,cellml/libcellml,nickerso/libcellml,nickerso/libcellml,cellml/libcellml,cellml/libcellml,hsorby/libcellml,hsorby/libcellml,nickerso/libcellml,cellml/libcellml