Produce IEEE compliant output from pow() despite platform deviations

src/cmd/ksh93/features/math.sh:
- Specify ast_float.h within iffehdrs instead of math.h, so that iffe
  will pick up on macro substitutions within libast. This should make
  any future efforts to remedy floating point behavior easier as well.
- Always include ast_float.h within the generated math header file,
  not just on IA64 platforms.

src/cmd/ksh93/tests/arith.sh:
- Test pow(1.0,-Inf) and pow(1.0,NaN) for IEEE compliance as well.
- Test the exponentiation operator (**) in addition, as streval.c,
  which processes the same, calls pow() separately.

src/lib/libast/features/float:
- Test the IEEE compliance of the underlying math library's pow()
  function and substitute macros producing compliant behavior if
  necessary.

src/lib/libast/features/float

@@ -1230,3 +1230,16 @@ tst	- -DSCAN=1 - -lm -DSTRTO=1 - -DMAC=1 - -DDIV=1 - -DEXP=1 - -DADD=1 - -DMPY=1
 		return 0;
 	}
 }end
+
+tst	ast_pow_ieee -lm note{ pow(1,inf) is IEEE compliant }end execute{
+	#include <sys/types.h>
+	#include <sys/stat.h>
+	#include <stdlib.h>
+	#include <unistd.h>
+	#include <math.h>
+	int main() { return pow(1.0, 1.0 / 0.0) != 1.0; }
+}end fail{
+	echo '#define powf(x,y)	(((x)==1.0)?1.0:powf((x),(y)))'
+	echo '#define pow(x,y)	(((x)==1.0)?1.0:pow((x),(y)))'
+	echo '#define powl(x,y)	(((x)==1.0)?1.0:powl((x),(y)))'
+}end