Initial support for C99's (or is it POSIX.1-2001's?) MATH_ERRNO,

MATH_ERREXCEPTION and math_errhandling, so that C99 applications at
least have the possibility of determining that errno is not set for
math functions.  Set math_errhandling to the non-standard-conforming
value of 0 for now to indicate that we don't support either method
of reporting errors.  We intentionally don't support MATH_ERRNO
because errno is a mistake, and we are missing support for
MATH_ERREXCEPTION (<fenv.h>, compiler support for <fenv.h>, and
actually setting the exception flags correctly).

lib/msun/src/math.h

@@ -40,6 +40,12 @@ extern const union __nan_un {
 #define	INFINITY	HUGE_VALF
 #define	NAN		(__nan.__uf)
 
+#if __ISO_C_VISIBLE >= 1999
+#define	MATH_ERRNO	1
+#define	MATH_ERREXCEPT	2
+#define	math_errhandling	0
+#endif
+
 /* Symbolic constants to classify floating point numbers. */
 #define	FP_INFINITE	0x01
 #define	FP_NAN		0x02