glapi: pass pointer size to python for glthread from meson

glthread (the python generator) needs to know the pointer size at compile
time to sort structure fields of calls for optimal structure packing based
on the CPU.

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27350>

meson.build

@@ -37,6 +37,8 @@ project(
 cc = meson.get_compiler('c')
 cpp = meson.get_compiler('cpp')
 
+sizeof_pointer = meson.get_compiler('c', native : true).sizeof('void*').to_string()
+
 null_dep = dependency('', required : false)
 
 if get_option('layout') != 'mirror'