Support for _Float16

[Archaversine]

I see that #52 adds support for _Float{32, 64, 128} which all seem to work, but there seems to be no support for _Float16. Is this something that can be added in?

[vmchale]

I've encountered something maybe related:

/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/math.h:614: (column 17) [ERROR]  >>> Syntax error !
  The symbol `__fabsf16' does not fit here.

[gwright83]

Earlier today I tested building a large project on macos 14.7.1/Xcode 16.1 using c2hs patched with jcmartin's update. It previously failed with the __fabsf16 does not fit here error; now it builds properly.

This seems to resolve the problem introduced (at least) by Apple's support of 16 bit floats in math.h.