fix nan/infinity macros in math.h, etc.

the previous version not only failed to work in c++, but also failed
to produce constant expressions, making the macros useless as
initializers for objects of static storage duration.

gcc 3.3 and later have builtins for these, which sadly seem to be the
most "portable" solution. the alternative definitions produce
exceptions (for NAN) and compiler warnings (for INFINITY) on newer
versions of gcc.

include/math.h

@@ -12,17 +12,18 @@ extern "C" {
 #define __NEED___uint64_t
 #include <bits/alltypes.h>
 
-#define __MAKE_FLOAT(i) (((union { int __i; float __f; }){ .__i = i }).__f)
-
-#define NAN       __MAKE_FLOAT(0x7fc00000)
-#define INFINITY  __MAKE_FLOAT(0x7f800000)
+#if 100*__GNUC__+__GNUC_MINOR__ >= 303
+#define NAN       __builtin_nanf("")
+#define INFINITY  __builtin_inff()
+#else
+#define NAN       (0.0f/0.0f)
+#define INFINITY  1e40f
+#endif
 
 #define HUGE_VALF INFINITY
 #define HUGE_VAL  ((double)INFINITY)
 #define HUGE_VALL ((long double)INFINITY)
 
-#define MAXFLOAT  __MAKE_FLOAT(0x7f7fffff)
-
 #define MATH_ERRNO  1
 #define MATH_EXCEPT 2
 #define math_errhandling 2
@@ -301,6 +302,7 @@ float       truncf(float);
 long double truncl(long double);
 
 #if defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE)
+#define MAXFLOAT        3.40282347e+38F
 #define M_E             2.7182818284590452354   /* e */
 #define M_LOG2E         1.4426950408889634074   /* log_2 e */
 #define M_LOG10E        0.43429448190325182765  /* log_10 e */