DOSbox builds well with Intel C++ 9.0 for Linux, and is
noticably faster than with GCC 4.0, especially in the
dynamic core, and especially after profile guided
optimization. (-prof-genx, -prof-use)
However there is a small hiccup that's due to the fact
that Intel C++ 9.0 was designed as a drop-in for GCC
3.4, not GCC 4.0. A compiler builtin is missing. DOSbox
doesn't use this builtin at all, but its absence causes
an error when you #include <cmath>.
This patch fixes that problem.