Update github actions workflow

- Uses matrix so that build steps don't need to be defined multiple
  times.
- Caches godot-cpp bindings, so they only need to be built when the
  submodule version changes.
- Uploads build artifacts for linux 32/64-bit, windows 64-bit and macOS
  64-bit.

addons/godot_xterm/native/SConstruct

@@ -69,11 +69,6 @@ Help(opts.GenerateHelpText(env))
 # Add PATH to environment so scons can find commands such as g++, etc.
 env.AppendENVPath('PATH', os.getenv('PATH'))
 
-# Generate godot-cpp bindings.
-# Options such as platform, target, etc. will be forwarded to the godot-cpp SConscript.
-ARGUMENTS['generate_bindings'] = True
-SConscript('external/godot-cpp/SConstruct')
-
 
 # Compile for Linux.
 if env['platform'] == 'linux':

addons/godot_xterm/native/build.sh

@@ -26,24 +26,10 @@ if [ ! -d "${GODOT_CPP_DIR}" ]; then
 	git submodule update --init --recursive -- $GODOT_CPP_DIR
 fi
 
+# Build godot-cpp bindings.
+cd ${GODOT_CPP_DIR}
+scons generate_bindings=yes -j$(nproc)
 
 # Build libgodot-xterm.
 cd ${NATIVE_DIR}
-case $1 in
-	"release-all")
-		# Cross-compile release build for all platforms.
-		scons platform=linux bits=64 target=release -j$(nproc)
-		if [ $IN_NIX_SHELL ]; then
-			nix-shell --pure --argstr system i686-linux --run "NIX_PATH=${NIX_PATH} scons platform=linux bits=32 target=release -j$(nproc)"
-		else
-			scons platform=linux bits=32 target=release -j$(nproc)
-		fi
-		scons platform=windows bits=64 target=release -j$(nproc)
-		#scons platform=windows bits=32 target=release -j$(nproc)
-		#scons platform=osx bits=64 target=release -j$(nproc)
-		;;
-	*)
-		# Default: Compile debug build for the current platform.
-		scons -j$(nproc)
-		;;
-esac
+scons -j$(nproc)