meson: enable cpp (optionally) for plugins

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Link: https://lore.kernel.org/qemu-devel/20260124182921.531562-9-pierrick.bouvier@linaro.org
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>

meson.build

@@ -77,7 +77,8 @@ python = import('python').find_installation()
 
 cc = meson.get_compiler('c')
 all_languages = ['c']
-if host_os == 'windows' and add_languages('cpp', required: false, native: false)
+enable_cpp = host_os == 'windows' or get_option('plugins')
+if enable_cpp and add_languages('cpp', required: false, native: false)
   all_languages += ['cpp']
   cxx = meson.get_compiler('cpp')
 endif