Enforce fast-path objc_msgSend() aka non-legacy dispatch

Forces Clang to use the fast path, which is not enabled by default on arm64 even though it's supported in the runtime.

Can be removed when Clang 18 containing this patch is available via the Android SDK:
llvm/llvm-project#76694

phases/20-gnustep-make.sh

@@ -19,13 +19,22 @@ mkdir -p "${INSTALL_PREFIX}"/etc/GNUstep
 GNUSTEP_USER_CONFIG_FILE="${INSTALL_PREFIX}"/etc/GNUstep/GNUstep-user.conf
 cp "${ROOT_DIR}"/config/gnustep-make-user.config "${GNUSTEP_USER_CONFIG_FILE}"
 
+OPTIONS=
+if [ "$ABI_NAME" == "arm64-v8a" ]; then
+	# enforce fast-path objc_msgSend() aka non-legacy dispatch (not enabled by default on arm64)
+	# can be removed when Clang 18 containing this patch is available via the Android SDK:
+	# https://github.com/llvm/llvm-project/pull/76694
+	OPTIONS="OBJCFLAGS=-fno-objc-legacy-dispatch"
+fi
+
 echo -e "\n### Running configure"
 ./configure \
   --host=${ANDROID_TARGET} \
   --prefix="${INSTALL_PREFIX}" \
   --with-library-combo=ng-gnu-gnu \
   --with-user-config-file="${GNUSTEP_USER_CONFIG_FILE}" \
   --with-runtime-abi=gnustep-2.0 \
+  ${OPTIONS}
 
 echo -e "\n### Installing"
 make install