meson.build: shut up a warning for the generated swig python wrapper

It's generated and it works, no need to have the missing-prototypes
warning on.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>

meson.build

@@ -565,6 +565,7 @@ shared_library(
    'libratbag',
    c_source,
    name_prefix: '_',
+   c_args : '-Wno-missing-prototypes',
    extra_files: [ i_source ] + src_libratbag ,
    dependencies: deps_libratbag + wrapper_deps,
    include_directories : include_directories('src', 'tools'),