Use proper types for meson objects

Fix invalid usage of meson objects which violates official meson
specification and thus breaks muon, an implementation of meson
written in C.

Reviewed-by: Mihai Preda <mhpreda@gmail.com>
Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15715>

meson_options.txt

@@ -357,7 +357,7 @@ option(
 option(
   'draw-use-llvm',
   type : 'boolean',
-  value : 'true',
+  value : true,
   description : 'Whether to use LLVM for the Gallium draw module, if LLVM is included.'
 )
 option(