Update meson.build

Author: dreamer-coding

meson.build

@@ -2,7 +2,7 @@ project('Fossil Test', 'c', 'cpp',
     meson_version: '>=1.2.0',
     license: 'MPL-2.0',
     version: '1.0.0',
-    default_options: ['c_std=c17', 'cpp_std=c++20'],)
+    default_options: ['c_std=c18', 'cpp_std=c++20'],)
 
 subdir('code')
 subdir('test')