Error in JIT-compile: TCNN_HALF_PRECISION not defined in JIT-kernel

It looks like the `TCNN_HALF_PRECISION` flag is not defined in the device code for the JIT-kernels, leading JIT-compilation to crash upon inclusion of `common.h`. ``` tiny-cuda-nn warning: JIT: compiling training_step_network_with_input_encoding.068edd8b68f80639.cu failed: tiny-cuda-nn/common.h(105): catastrophic error: #error directive: "TCNN_HALF_PRECISION is undefined. The build system must define this explicitly." #error "TCNN_HALF_PRECISION is undefined. The build system must define this explicitly." ^ 1 catastrophic error detected in the compilation of "training_step_network_with_input_encoding.068edd8b68f80639.cu". Compilation terminated. Failed to JIT-compile `training_step_network_with_input_encoding`. Disabling JIT. ```