tests: always make bundles, adapt build and tests

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 6897aeb105 #17468

Closes #17590

tests/unit/README.md

@@ -45,7 +45,27 @@ and the `tests/FILEFORMAT.md` documentation.
 
 For the actual C file, here's a simple example:
 ~~~c
+    #include "curlcheck.h"
 
+    #include "a libcurl header.h" /* from the lib dir */
+
+    static CURLcode test_unit9998(char *arg)
+    {
+      UNITTEST_BEGIN_SIMPLE
+
+      /* here you start doing things and checking that the results are good */
+
+      fail_unless( size == 0 , "initial size should be zero" );
+      fail_if( head == NULL , "head should not be initiated to NULL" );
+
+      /* you end the test code like this: */
+
+      UNITTEST_END_SIMPLE
+    }
+~~~
+
+Here's an example using optional initialization and cleanup:
+~~~c
     #include "curlcheck.h"
 
     #include "a libcurl header.h" /* from the lib dir */
@@ -61,7 +81,9 @@ For the actual C file, here's a simple example:
       /* done before shutting down and exiting */
     }
 
-    UNITTEST_START
+    static CURLcode test_unit9999(char *arg)
+    {
+      UNITTEST_BEGIN(unit_setup())
 
       /* here you start doing things and checking that the results are good */
 
@@ -70,4 +92,6 @@ For the actual C file, here's a simple example:
 
       /* you end the test code like this: */
 
-    UNITTEST_STOP
+      UNITTEST_END(unit_stop())
+    }
+~~~