Dump the return type of functions in gimple dumps

Dump the return type of functions in gimple dumps

gcc/
	* tree-cfg.c (dump_function_to_file): Dump the return type of
	functions, in a line to itself before the function body, mimicking
	the layout of a C function.

gcc/testsuite/
	* gcc.dg/tree-ssa/pr23401.c: Update the expected number of
	occurrences of "int" in the gimple dump to reflect that the return
	types of functions now show up in such dumps.
	* gcc.dg/tree-ssa/pr27810.c: Likewise.

From-SVN: r209902