libstdc++: Do not use off64_t in calls to copy_file_range [PR110462]

Although the copy_file_range(2) man page shows the arguments as off64_t*
that is not portable. For musl there is no off64_t type, as off_t is
always 64-bit. Use the loff_t type which is always 64-bit even if off_t
isn't. We could just use off_t because the filesystem library is
compiled with _FILE_OFFSET_BITS=64, but loff_t is the more correct type
for this interface.

libstdc++-v3/ChangeLog:

	PR libstdc++/110462
	* acinclude.m4 (GLIBCXX_CHECK_FILESYSTEM_DEPS): Check that
	copy_file_range can be called with loff_t* arguments.
	* configure: Regenerate.
	* src/filesystem/ops-common.h (copy_file_copy_file_range):
	Use loff_t for offsets.