This avoids stuff like
/usr/include/c++/4.0.0/cmath:85: error: template with C linkage
/usr/include/c++/4.0.0/cmath: In function 'float std::abs(float)':
/usr/include/c++/4.0.0/cmath:92: error: declaration of C function 'float
std::abs(float)' conflicts with
/usr/include/c++/4.0.0/cmath:88: error: previous declaration 'double
std::abs(double)' here
This was SVN commit r4291.