Use combined_fn in tree-vrp.c

Use combined_fn in tree-vrp.c

Another patch to extend uses of built_in_function to combined_fn, this time
in tree-vrp.c.

Tested on x86_64-linux-gnu, aarch64-linux-gnu and arm-linux-gnueabi.

gcc/
	* tree-vrp.c: Include case-cfn-macros.h.
	(extract_range_basic): Switch on combined_fn rather than handling
	built-in functions and internal functions separately.

From-SVN: r230479