Use of libdl is optional. Closes #248.

manual tests/1 wrap/meson.build

@@ -2,10 +2,13 @@ project('downloader', 'c')
 
 s = subproject('sqlite')
 
+libdl = find_library('dl', required : false)
+
 e = executable('dtest', 'main.c',
   include_directories : s.get_variable('sqinc'),
-link_args : ['-pthread', '-ldl'],
+  link_args : ['-pthread'],
   c_args : '-pthread',
+  dependencies : libdl,
   link_with : s.get_variable('sqlib'))
 
 test('dltest', e)