Mesa/src/mesa/tnl/t_vb_arbprogram.c contains this bit of code in do_LOG():

#ifdef _WIN32
   GLfloat mantissa = (GLfloat) frexp((double)tmp, &exponent);
#else
   GLfloat mantissa = frexpf(tmp, &exponent);
#endif

Unfortunately, it's not just Win32 but older Unixes that don't have frexpf().
(It was added in C99 and Unix 2003 standards, but not included in older 
standards.)

For instance, this causes Xorg CVS head builds to fail on Solaris 9 (which only
had C89/Unix 98 compliance), but not Solaris 10 and later (which added C99 &
Unix 2003 compliance).

It would be nice if this #ifdef could be changed instead to 
#ifdef HAVE_FREXPF or something similar that could be set by the build system
(including Imake/autoconf in the Xorg builds which include Mesa).