* include/experimental/bits/fs_path.h (__is_path_src)
	(_S_range_begin, _S_range_end): Overload to treat string_view as a
	Source object.
	(path::operator+=, path::compare): Overload for basic_string_view.
	* testsuite/experimental/filesystem/path/construct/string_view.cc:
	New test.
	* testsuite/experimental/filesystem/path/construct/
	string_view_cxx17.cc: New test.

From-SVN: r241658