Exposition-Only Members Without \exposid

[RobertLeahy]

• source_location [support.srcloc.class.general]
• partial_ordering [cmp.partialord]
• weak_ordering [cmp.weakord]
• basic_backtrace [stacktrace.basic.overview]

[JohelEGP]

See #4702.

[RobertLeahy]

• basic_istringstream [istringstream.general]
• basic_ostringstream [ostringstream.general]
• basic_stringstream [stringstream.general]
• basic_ispanstream [ispanstream.general]
• basic_ospanstream [ospanstream.general]
• basic_spanstream [ospanstream.general]

[frederick-vs-ja]

There're many exposition-only names that are not \exposid'd in [time].