log2 and log2f are required by C99 and are not implemented.
Workaround the deficiency.

--- lib/msun/src/math.h.old	2010-03-14 17:02:25.000000000 +0100
+++ lib/msun/src/math.h	2010-03-14 17:07:03.000000000 +0100
@@ -203,6 +203,7 @@
 double	frexp(double, int *);	/* fundamentally !__pure2 */
 double	ldexp(double, int);
 double	log(double);
+#define log2(x) log(x)/log(2.0)
 double	log10(double);
 double	modf(double, double *);	/* fundamentally !__pure2 */
 
@@ -319,6 +320,7 @@
 float	log10f(float);
 float	log1pf(float);
 float	logf(float);
+#define log2f(x) logf(x)/logf(2.0)
 float	modff(float, float *);	/* fundamentally !__pure2 */
 
 float	powf(float, float);