Problems compiling with recent GCC (>= 6.1 or so)

[Cat-Ion]

Some combination of our atan2 implementation and the builtin clz causes recent gcc to die with an internal compiler error (https://gcc.gnu.org/ml/gcc-bugs/2017-08/msg01578.html).

[Cat-Ion]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82025
Apparently fixed in gcc 8