Similar to my patches for HUGE_VAL and INFINITY. this patch eliminates
the bits/nan.h headers. __builtin_nanf ("") is used to define NAN for
GCC 3.3 and later; the fallback is (0.0f / 0.0f), which is a constant
expression for a quiet NaN of type float, but raises a spurious
"invalid" exception outside static initializers, which seems the best
that can be done purely in standard C. Again, if anyone actually uses
a compiler with its own incompatible extension for producing a
constant quiet NaN, we can add compiler conditionals.
Tested for x86_64.
* math/math.h [__USE_ISOC99] (NAN): Define directly here. Do not
include <bits/nan.h>.
* math/Makefile (headers): Remove bits/nan.h.
* bits/nan.h: Remove.
* sysdeps/ieee754/bits/nan.h: Likewise.
* sysdeps/mips/bits/nan.h: Likewise.
c0c49d60cf