complex support routines

[Jan Beulich]

libstdc++'s complex header makes unconditional use of functions like
__builtin_cabs[fl], which the compiler may (have to) expand to a
function call to the normal (C99) function. However, not all platforms
support this, and libmath support for all of the complex functions
appears to have benn removed in late 2000. What I'd like to understand
is how I'm supposed to use complex functions on a system that does not
fully (or not at all) support C99 math/complex functionality.

Thanks, Jan