globally.  Instead of using "#define _GNU_SOURCE" in the source code
files, we use "KDE_CXXFLAGS = -D_GNU_SOURCE" in kstars/kstars/Makefile.am.
(_GNU_SOURCE is needed when including math.h so we get the GNU function
"sincos()", if it is available).

This allows the non-INDI code to compile cleanly with "enable-final"
active (recall that we have disabled enable-final in the INDI directory).

Will backport to KDE_3_2_BRANCH as well.

CCMAIL: kstars-devel@kde.org
CCMAIL: l.savernik@aon.at

svn path=/trunk/kdeedu/kstars/; revision=285168