re PR c/27273 (tree check fail for legal code when convert returns a constant from an expression that was not constant)

        PR c/27273
        * c-common.c (convert_and_check): only track TREE_CONSTANT_OVERFLOW
        for CONSTANT_CLASS_P expressions.

        * gcc.dg/overflow-warn-5.c: New testcase.

From-SVN: r114238