Fix gnulib's lstat replacement in C++ namespace mode

Fix gnulib's lstat replacement in C++ namespace mode

Fixes:

 unittests/string_view-selftests.c: In member function 'gnulib::_gl_lstat_wrapper::operator gnulib::_gl_lstat_wrapper::type() const':
 unittests/string_view-selftests.c:11432:22: error: expected primary-expression before ';' token
      return ::rpl_stat;
		       ^

The problem is that the lstat replacement depends on the stat
(function) declaration, which is only declared afterwards.  The fix is
simply to declare lstat after stat.