always use newest appimagetool version (scp-fs2open#7468)

This will download the appimagetool utility as part of the install step so
that the newest version of both the tool and the runtime is always used. Moving
it out of the build image allows us to take advantage of newer capabilities,
such as no longer having an external dependency on libfuse2.

Author: notimaginative

ci/linux/generate_appimage.sh

@@ -2,13 +2,37 @@
 
 INSTALL_FOLDER=$1
 
+# safety check
+if [ ! -d bin -o ! -f cmake_install.cmake ]; then
+	echo "ERROR! This script must be run from within the build root!"
+	exit 1
+fi
+
+if [ ! -x "$(which wget)" ]; then
+	echo "ERROR! Required utility is not available: wget"
+	exit 1
+fi
+
+# install newest appimagetool if it's not already available
+if [ ! -x ./bin/appimagetool ]; then
+	APPIMAGE_TOOL_URL="https://github.com/AppImage/appimagetool/releases/download/continuous/appimagetool-$(uname -m).AppImage"
+
+	wget -O ./bin/appimagetool "$APPIMAGE_TOOL_URL" || { echo "ERROR! Failed to get appimagetool!" && exit 1; }
+	chmod +x ./bin/appimagetool
+fi
+
+# This shouldn't be needed with newer runtimes, but they still generate an
+# error if fusermount is missing even though it works. So to skip error msg
+# and have max compatibility with runtimes and containers we'll use it.
+export APPIMAGE_EXTRACT_AND_RUN=1
+
 # Install Freespace2 targets
 cmake -DCMAKE_INSTALL_PREFIX=$INSTALL_FOLDER/Freespace2 -DCOMPONENT=Unspecified -P cmake_install.cmake
 cmake -DCMAKE_INSTALL_PREFIX=$INSTALL_FOLDER/Freespace2 -DCOMPONENT=Freespace2 -P cmake_install.cmake
 
 # We need to be a bit creative for determining the AppImage name since we don't want to hard-code the name
 FILENAME="$(find $INSTALL_FOLDER/Freespace2/bin -name 'fs2_open_*' -type f -printf "%f\n").AppImage"
-appimagetool -n "$INSTALL_FOLDER/Freespace2" "$INSTALL_FOLDER/$FILENAME"
+./bin/appimagetool -n "$INSTALL_FOLDER/Freespace2" "$INSTALL_FOLDER/$FILENAME"
 chmod +x "$INSTALL_FOLDER/$FILENAME"
 
 # Maybe install qtFRED targets
@@ -18,7 +42,7 @@ if [ -f qtfred/cmake_install.cmake ]; then
 
 	# We need to be a bit creative for determining the AppImage name since we don't want to hard-code the name
 	FILENAME="$(find $INSTALL_FOLDER/qtFRED/bin -iname 'qtfred_*' -type f -printf "%f\n").AppImage"
-	appimagetool -n "$INSTALL_FOLDER/qtFRED" "$INSTALL_FOLDER/$FILENAME"
+	./bin/appimagetool -n "$INSTALL_FOLDER/qtFRED" "$INSTALL_FOLDER/$FILENAME"
 	chmod +x "$INSTALL_FOLDER/$FILENAME"
 fi