Fix illegal instruction crash on x64 CPUs without POPCNT instruction when compiled with MSVC
MSVC doesn't check for HW support for POPCNT instruction and so GTK compiled with it crashes when run on CPUs like Core2.
Here's a link to the same problem being fixed for the Qt project: https://codereview.qt-project.org/c/qt/qtbase/+/183633/3/src/corelib/tools/qalgorithms.h#651