Bump required C standard version to C11

dnicolodi · dnicolodi · commit 8eee488f29cd · 2024-10-15T14:37:50.000+02:00
This solves a compilation error with Python 3.13-rc1 on macOS. The
issue is solved in 3.13-rc2 but requiring C11 does not have any
drawback.
diff --git a/meson.build b/meson.build
@@ -7,7 +7,7 @@ project(
   meson_version: '>= 1.0.0',
   default_options: [
     'buildtype=release',
-    'c_std=c99',
+    'c_std=c11',
   ]
 )
 
