Merge r1480077 from trunk:

 * r1480077
   Check separately for -flto and -Wno-clobbered with --enable-optimize.
   Justification:
     The -flto flag was not used by older compilers that do not
     suport -Wno-clobbered, even when they do support -flto.
   Votes:
     +1: brane (for 1.8.1)
     +1: rhuijben, cmpilato



git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1482455 13f79535-47bb-0310-9956-ffa450edef68