Specify '-optimize-size' only when building release binaries

This is a follow up to my previous commit [1], which started specifying
'-optimize-size' configure option for Qt6 for google#822.

It turns out that configure process may fail if '-optimize-size' is not
specified with either '-release' or '-debug-and-release'.

This commit takes care of such a limitation.

 [1]: 5757f28

PiperOrigin-RevId: 575634660

src/build_tools/build_qt.py

@@ -262,7 +262,6 @@ def make_configure_options(args: argparse.Namespace) -> list[str]:
 
   qt_configure_options = ['-opensource',
                           '-c++std', 'c++20',
-                          '-optimize-size',
                           '-silent',
                           '-no-cups',
                           '-no-dbus',
@@ -362,6 +361,9 @@ def make_configure_options(args: argparse.Namespace) -> list[str]:
   elif args.release:
     qt_configure_options += ['-release']
 
+  if args.release:
+    qt_configure_options += ['-optimize-size']
+
   qt_src_dir = pathlib.Path(args.qt_src_dir).resolve()
   qt_dest_dir = pathlib.Path(args.qt_dest_dir).resolve()
   if qt_src_dir != qt_dest_dir: