[Bug c/59871] [4.7/4.8/4.9 Regression] No unused value warning for comma expression

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59871

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
And similarly in emit_side_effect_warnings, if there are TREE_SIDE_EFFECTS, but
the expr is COMPOUND_EXPR, find the rightmost operand of the nested
COMPOUND_EXPRs and if it doesn't have TREE_SIDE_EFFECTS, warn similarly.