The main issue is many compilers have issues on x86 platforms due to Intel's bizarre slowness in defining how to pass fp16 parameters in their official ABI.
Intel support is a bit more dubious, especially if you're stuck on older LLVM versions, but __fp16 works for most purposes if all you want is storage. You just have to pass any fp16 function parameters as pointers/references to work around the aforementioned ABI issue. Architecturally intel has supported fp16 conversions necessary for __fp16 for quite a while now, so no reason for it not to work (whereas full fp16 arithmetic is restricted to some less common variants of avx512 iirc, so the distinction between __fp16 and _Float16 isn't much on most intel systems).
It should be fairly straightforward to write a quick test program and see what your local compilers can cope with.