gears: Don't enable experimental glm functions
Fixes compilation error on ubuntu 18.04.
In file included from ../src/pipeline_gears.cpp:13: In file included from ../src/pipeline_gears.hpp:15: In file included from ../src/gear.hpp:14: In file included from ../src/glm_inc.hpp:18: In file included from /usr/include/glm/gtx/string_cast.hpp:23: In file included from /usr/include/glm/gtx/../gtx/dual_quaternion.hpp:274: /usr/include/glm/gtx/dual_quaternion.inl:31:20: error: use of undeclared identifier 'P' : real(tquat<T, P>()) ^ /usr/include/glm/gtx/dual_quaternion.inl:32:20: error: use of undeclared identifier 'P' , dual(tquat<T, P>(0, 0, 0, 0)) ^