And add std.math.f128_* constants.
The routines are:
__fixdfdi, __fixdfsi, __fixdfti,
__fixsfdi, __fixsfsi, __fixsfti,
__fixtfdi, __fixtfsi, __fixtfti.
These all call fixint which is a generic zig function that does the
conversion:
pub fn fixint(comptime fp_t: type, comptime fixint_t: type, a: fp_t) fixint_t
There are also a set tests:
__fixdfdi_test, __fixdfsi_test, __fixdfti_test,
__fixsfdi_test, __fixsfsi_test, __fixsfti_test,
__fixtfdi_test, __fixtfsi_test, __fixtfti_test.