When sleeping after commit/update use wcroot paths if possible
as they will not have been removed by the operation.  This enables
the shorter sleep in more cases.

* subversion/libsvn_client/commit.c
  (svn_client_commit6): Get wcroot path if possible.

* subversion/libsvn_client/update.c
  (svn_client_update4): Get wcroot path if possible.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1508438 13f79535-47bb-0310-9956-ffa450edef68
Follow-up to r1508221.

* build/ac-macros/svn-macros.m4
  (SVN_CHECK_FOR_DUNDER_BUILTINS): make the cross-compile case match the
                                   standard check
* configure.ac
  (SVN_CHECK_FOR_DUNDER_BUILTINS): update comment

Found by: danielsh

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1508458 13f79535-47bb-0310-9956-ffa450edef68