libstdc++/7680: float functions undefined in math.h/cmath with #define _XOPEN_SOURCE

[ljrittle@gcc.gnu.org]

Synopsis: float functions undefined in math.h/cmath with #define _XOPEN_SOURCE

Responsible-Changed-From-To: unassigned->ljrittle
Responsible-Changed-By: ljrittle
Responsible-Changed-When: Wed Mar 26 10:41:24 2003
Responsible-Changed-Why:
    Mine.
State-Changed-From-To: open->analyzed
State-Changed-By: ljrittle
State-Changed-When: Wed Mar 26 10:41:24 2003
State-Changed-Why:
    This is a well-known issue (and not just with FreeBSD).  Although (1) it is a bug with the configure script itself to test for "feature macros" in a different context than will be used, (2) it is a libstdc++-v3 bug to not adapt to visibility of the underlying libc.  I have assigned myself (and left it open) since I am reworking this aspect of the C++ library.  I suspect that even after I fix (2), (1) will still present a problem
    for some software packages.
    
    I can confirm that this bug still exists in 3.2.2 and mainline.  Thanks for
    the report.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7680