Enable x86_64 builds of libcellml with cibuildwheel for python 3.7 and 3.8.
Enable x86_64 builds of libcellml with cibuildwheel for python 3.7 and 3.8.

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