re PR c/89946 (ICE in assemble_start_function, at varasm.c:1871)

re PR c/89946 (ICE in assemble_start_function, at varasm.c:1871)

	PR c/89946
	* varasm.c (assemble_start_function): Don't use tree_fits_uhwi_p
	and gcc_unreachable if it fails, just call tree_to_uhwi which
	verifies that too.  Test TREE_CHAIN instead of list_length > 1.
	Start warning message with a lower-case letter.  Formatting fixes.
c-family/
	* c-attribs.c (handle_patchable_function_entry_attribute): Add
	function comment.  Warn if arguments of the attribute are not positive
	integer constants.
testsuite/
	* c-c++-common/pr89946.c: New test.

From-SVN: r270305