include: Correct _IEEE_754_2008_SNAN for MIPS NAN2008 variant

Later MIPS processors have a NAN2008 option that allows it's
FPU implementation to be IEEE 754-2008 comformance. This can
be detected at build time with __mips_nan2008 macro.

Only define _IEEE_754_2008_SNAN to 0 when __mips_nan2008 is
not defined.

Signed-off-by: Jiaxun Yang <[email protected]>

Author: FlyGoat

newlib/libc/include/machine/ieeefp.h

@@ -333,7 +333,9 @@ warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 #endif
 
 #ifdef __mips__
+#ifndef __mips_nan2008
 #define _IEEE_754_2008_SNAN 0
+#endif
 #ifndef __mips_soft_float
 #define _SUPPORTS_ERREXCEPT
 #endif