libstdc++: Simplify basic_string_view::ends_with [PR 101361]

libstdc++: Simplify basic_string_view::ends_with [PR 101361]

The use of npos triggers a diagnostic as described in PR c++/101361.
This change replaces the use of npos with the exact length, which is
already known. We can further simplify it by inlining the effects of
compare and substr, avoiding the redundant range checks in the latter.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
libstdc++-v3/ChangeLog:

	PR c++/101361
	* include/std/string_view (ends_with): Use traits_type::compare
	directly.

(cherry picked from commit 4d3eaeb4f505b0838c673ee28e7dba8687fc8272)