* Generalise NaN handling and make std.math.nan() give quiet NaNs
* Address uses of std.math.qnan_* and std.math.nan_* consts
* Comment out failing test due to issues with signalling NaN
* Fix issue in c_builtins.zig where we need qnan_u32
@bitCast from integer NaN representation to float NaN resulted in
changed bits in float. This only happened with signaled NaN.
- added test for signaled NaN
- added tests for quiet NaN (for completeness)
closes#14198