Import patch from mainline to fix gold's handling of already versioned symbols.
    
    gold	PR gold/23409
    	* symtab.cc (Symbol_table::define_special_symbol): Add check for
    	version name on existing symbol.
    	* testsuite/Makefile.am (ver_test_pr23409): New test case.
    	* testsuite/Makefile.in: Regenerate.
    	* testsuite/ver_test_pr23409.sh: New test script.
    	* testsuite/ver_test_pr23409_1.script: New version script.
    	* testsuite/ver_test_pr23409_2.script: New version script.