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/unit2601.c

@@ -27,16 +27,6 @@
 #include "bufq.h"
 #include "curl_trc.h"
 
-static CURLcode unit_setup(void)
-{
-  CURLcode res = CURLE_OK;
-  return res;
-}
-
-static void unit_stop(void)
-{
-}
-
 static const char *tail_err(struct bufq *q)
 {
   struct buf_chunk *chunk;
@@ -86,12 +76,12 @@ static void dump_bufq(struct bufq *q, const char *msg)
   curl_mfprintf(stderr, "- spares: %zu\n", n);
 }
 
-static unsigned char test_data[32*1024];
-
 static void check_bufq(size_t pool_spares,
                        size_t chunk_size, size_t max_chunks,
                        size_t wsize, size_t rsize, int opts)
 {
+  static unsigned char test_data[32*1024];
+
   struct bufq q;
   struct bufc_pool pool;
   size_t max_len = chunk_size * max_chunks;
@@ -250,7 +240,10 @@ static void check_bufq(size_t pool_spares,
     Curl_bufcp_free(&pool);
 }
 
-UNITTEST_START
+static CURLcode test_unit2601(char *arg)
+{
+  UNITTEST_BEGIN_SIMPLE
+
   struct bufq q;
   ssize_t n;
   CURLcode result;
@@ -278,4 +271,5 @@ UNITTEST_START
   check_bufq(8, 8000, 10, 1234, 1234, BUFQ_OPT_NONE);
   check_bufq(8, 1024, 4, 129, 127, BUFQ_OPT_NO_SPARES);
 
-UNITTEST_STOP
+  UNITTEST_END_SIMPLE
+}