why do we need FINITE_P?

[Janis Johnson]

Why does a build of libstdc++-v3 require FINITE_P to be defined?

On DYNIX/ptx (based on svr4) there is no C99 support, and none of the
functions that might be used to determine whether a value is finite are
found during configuration.  A build of libstdc++-v3 fails at line 151
of libstdc++-v3/libmath/mathconf.h with #error "We need FINITE_P".

I tried defining FINITE_P(X) to be finite(X), and that works fine even
though there is no function called finite() in any of the libraries.
The build of libstdc++ succeeds, and there are no c++ tests that fail
due to finite() not being available.

There are probably other operating systems that have the same problem
when the native libc is used.  Is there a requirment that the new
libstdc++ support functionality from C99 as well as from the C++
standard?  If not, can mathconf.h be changed so it doesn't require this
functionality?

Janis Johnson