For PR60531, GCC wrongly rejects function templates with explicitly
specified template arguments as overloaded. They are resolved by
resolve_nondeduced_context, which is normally called by
cp_default_conversion through decay_conversion, but the latter have
extra effects making them unusable here. Calling the former directly
does work.
* typeck.c (cp_build_binary_op): See if overload can be resolved.
(cp_build_unary_op): Ditto.
* g++.dg/template/operator15.C: New test.
From-SVN: r271910
