functions.sh generate_appimage GLIBC_NEEDED set after first use

[schuhschuh]

Posted this first in https://github.com/AppImage/AppImageKit/issues/432, i.e., wrong project.

generate_appimage in https://raw.githubusercontent.com/AppImage/AppImages/master/functions.sh sets GLIBC_NEEDED before first use (rm old output):

rm ../out/$APP"-"$VERSION".glibc"$GLIBC_NEEDED"-"$ARCH".AppImage" 2>/dev/null || true
GLIBC_NEEDED=${GLIBC_NEEDED:=$(glibc_needed)}
./AppImageAssistant ./$APP.AppDir/ ../out/$APP"-"$VERSION".glibc"$GLIBC_NEEDED"-"$ARCH".AppImage"

Aside: Just started to see if I can package our MIRTK command line tools with this as previously suggested by @probonopd (see here). First likely failing script: make_appimage.sh. Hence, not quite familiar yet with how to create an AppImage from a Travis CI build... anyway that's getting off topic ;-).