tests: drop mk-bundle exceptions

Using a mixture of techniques to avoid symbols collisions:
- reduce scope.
- add `t*_` / `T*_` prefix.
- move shared functions to `testutil.c`.
  (`suburl()`, `rlim2str()`)
- clone re-used lib*.c sources.
  (lib587, lib645)
- include shared symbols just once in re-used `lib*.c` sources.
  (using `LIB*_C` guards.)
- drop re-used `lib*.c` sources where they were identical or
  unused.
- make macros global.
- #undef macros before use.

What remain is the entry functions `test`, and `unit_setup`,
`unit_stop` in unit tests.

Also:
- fix formatting and other minor things along the way.
- add `const` where possible.
- sync some symbol names between tests.
- drop `mk-bundle-hints.sh` that's no longer necessary.

Closes #17468

tests/data/test1596

@@ -28,7 +28,7 @@ http
 HTTP Retry-After header parsing using a date
 </name>
 <tool>
-lib%TESTNUMBER
+lib1594
 </tool>
 <command>
 http://%HOSTIP:%HTTPPORT/%TESTNUMBER