tests: always make bundles, adapt build and tests

[vszakats]

Make test bundles the default. Drop non-bundle build mode.
Also do all the optimizations and tidy-ups this allows, simpler builds,
less bundle exceptions, streamlined build mechanics.

Also rework the init/deinit macro magic for unit tests. The new method
allows using unique init/deinit function names, and calling them with
arguments. This is in turn makes it possible to reduce the use of global
variables.

Note this drop existing build options -DCURL_TEST_BUNDLES= from cmake
and --enable-test-bundles / --disable-test-bundles from autotools.

Also:

• rename test entry functions to have unique names: test_<testname>
  This removes the last exception that was handled in the generator.
• fix make dist to not miss test sources with test bundles enabled.
• sync and merge tests/mk-bundle.pl into scripts/mk-unity.pl.
• mk-unity.pl: add --embed option and use it when CURL_CLANG_TIDY=ON
  to ensure that clang-tidy does not miss external test C sources.
  (because clang-tidy ignores code that's #included.)
• tests/unit: drop no-op setup/stop functions.
• tests: reduce symbol scopes, global macros, other fixes and tidy-ups.
• tool1621: fix to run, also fix it to pass.
• sockfilt: fix Windows compiler warning in certain unity include order,
  by explicitly including warnless.h.

Follow-up to 6897aeb #17468

---

w/o ws: https://github.com/curl/curl/pull/17590/files?w=1

• perhaps first drop all build-time duplicated libtests sources. (Also maybe apply that to the two sources that I cloned in 6897aeb tests: drop mk-bundle exceptions #17468: lib587, lib645.) It would simplify this PR. → libtests: stop building the sames source multiple times #17598
• fix breaking some autotools magic that included the test .c source in the distro before this patch, but no longer with bundles enabled. I suspect bundle never worked for dist, but went unnoticed because it wasn't CI tested.
  Also check unity for the same issue.
• try dropping non-bundle build logic.
• try dropping mk-bundle script. [dropped one of the two.]
  While the script is adding some build complexity, overall it seems to save some manual labour/annoyance when adding/deleting scripts.
  Also, the script is also used for unity anyway, and the script is required to embed sources for clang-tidy. The latter isn't something
  solvable without it, unless clang-tidy gets fixed to not ignore #included C sources.
• make entry functions static.
• give entry functions explicit unique names.
• caveat: clang-tidy excludes included .c sources from its checks. Fixed by adding an 'embed' mode and enabling it when building with CURL_CLANG_TIDY=ON.
• drop remaining mk-bundle script? It'll add more manual management, but simplifies the build mechanics.
  mk-bundle also has a "unity" feature for the misc test source, with autotools. [FUTURE PR]
  update: snag: make dist is tricky in this case, and adds an extra manual "accounting" job: add to the bundle file twice, then add to Makefile.inc too.
• it would seem to make sense to drop a whole bunch of per-test #includes to make everything shorter and more efficient. [FUTURE: this can be done as we go. There isn't much to save in terms of build perf, but might be useful to make the test snippets simpler, shorted.]
• and/or rework or add mk-bundle option to include the files instead of #include-ing them. To keep them friendly with clang-tidy. [DONE]
• is there any downside/upside of just always embedding, insead of #including? [→ let's keep #include-ing by default for now] update: Yes there is: the compiler messages refer to the generated source, so the filenames and line numbers become useless, the only way to figure out where the issue is is by looking at the (hopefully included) code snippet.
• issue: unit_setup(), unit_stop() are referenced from a macro. Making these names unique for each test is still a head-scratcher. Perhaps just removing this macro magic may work? It'd also allow to make some statics local and not stomp on the global namespace. They are an init block with error handling and a deinit block with predefined goto target, used by helper macros.

#define UNITTEST_START                          \
  CURLcode test(char *arg)                      \
  {                                             \
    (void)arg;                                  \
    if(unit_setup()) {                          \
      fail("unit_setup() FAILURE");             \
    }                                           \
    else {

#define UNITTEST_STOP                           \
    goto unit_test_abort; /* avoid warning */   \
unit_test_abort:                                \
    unit_stop();                                \
  }                                             \
  return (CURLcode)unitfail;                    \
  }