GCC and Clang/LLVM will support _Float16 on X86 in C/C++, following
the latest X86 psABI. (https://gitlab.com/x86-psABIs)
_Float16 arithmetic will be performed using native half-precision. If
native arithmetic instructions are not available, it will be performed
at a higher precision (currently always float) and then truncated down
to _Float16 immediately after each single arithmetic operation.