Fix build for legacy distributions

The readline module is part of Python itself, but it must be required
explicitly on newer distributions (16.0, Factory). However, Python
packages in older distributions (15.x and earlier) do not have the
corresponding Provides. :-(

Solve it by Build-requiring %pythons. Yes, it does bring a lot of
unneded stuff into the build environment...

Signed-off-by: Petr Tesarik <ptesarik@suse.com>

python-drgn.spec

@@ -25,8 +25,8 @@ Group:          Development/Tools/Debuggers
 URL:            https://github.com/osandov/drgn
 Source:         drgn-%{version}.tar.xz
 BuildRequires:  %{python_module devel}
-BuildRequires:  %{python_module readline}
 BuildRequires:  %{python_module setuptools}
+BuildRequires:  %{pythons}
 BuildRequires:  autoconf
 BuildRequires:  automake
 BuildRequires:  check-devel