Minor tidy up for clang-tidy around CMake if statements.
Minor tidy up for clang-tidy around CMake if statements.

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