re PR c++/54537 (undiagnosed using-declaration conflicting with used function)

gcc/cp/
        PR c++/54537
        * cp-tree.h: Check OVL_USED with OVERLOAD_CHECK.
        * name-lookup.c (do_nonmember_using_decl): Make sure we have an
	OVERLOAD before calling OVL_USED. Call diagnose_name_conflict
	instead of issuing an error without mentioning the conflicting
	declaration.

libstdc++-v3/
        PR c++/54537
	* include/tr1/cmath: Remove pow(double,double) overload, remove a
	duplicated comment about DR 550. Add a comment to explain the
	issue.
	* testsuite/tr1/8_c_compatibility/cmath/pow_cmath.cc: New.

gcc/testsuite/
        PR c++/54537
        * g++.dg/overload/using3.C: New.
	* g++.dg/overload/using2.C: Adjust.
	* g++.dg/lookup/using9.C: Likewise.

Co-Authored-By: Peter Bergner <bergner@vnet.ibm.com>

From-SVN: r201414