PR c/48418
* c-common.c (c_fully_fold_internal): Warn for LSHIFT_EXPR and
RSHIFT_EXPR, if orig_op1 isn't INTEGER_CST, op1 is INTEGER_CST
and is either negative or bigger or equal to type precision
of the first operand.
* typeck.c (cp_build_binary_op): For LSHIFT_EXPR and RSHIFT_EXPR,
call maybe_constant_value for the negative or too big shift
count warnings.