* fold-const.c (const_binop): Avoid performing the FP operation at
	compile-time, if either operand is NaN and we honor signaling NaNs,
	or if we're dividing by zero and either flag_trapping_math is set
	or the desired mode doesn't support infinities.
	(fold_initializer): New function to fold an expression ignoring any
	potential run-time exceptions or traps.
	* tree.h (fold_initializer): Prototype here.
	* c-typeck.c (build_binary_op): Move to the end of the file so
	that intializer_stack is in scope.  If constructing an initializer,
	i.e. when initializer_stack is not NULL, use fold_initializer to
	fold expressions.
	* simplify-rtx.c (simplify_binary_operation): Likewise, avoid
	performing FP operations at compile-time, if they would raise an
	exception at run-time.

From-SVN: r69533