Drop -ansi from the default CXXFLAGS.

In preparation for making having the default CXXFLAGS available on all
systems using GCC instead of only Linux/Hurd, remove -ansi from the
CXXFLAGS.

strtoll(3), used, for example, in kdelibs, is part of C99; -ansi means
GCC will switch to C89 and C++98, which breaks things on systems such
as FreeBSD. It worked on glibc-based systems because libstdc++ always
defines _GNU_SOURCE on Linux, which ends up enabling additional
features.

This change should not break existing code, as dropping -ansi actually
means being less strict than before.

Discussed in the kde-buildsystem mailing list [1].

[1] http://lists.kde.org/?t=134482883000001&r=1&w=2

CCMAIL: kde-buildsystem@kde.org