Before this patch `ENABLE_DEBUG=ON` always enabled the TrackMemory
(aka `ENABLE_CURLDEBUG=ON`) feature, but required the `Debug` CMake
configration to actually enable curl debug features
(aka `-DDEBUGBUILD`).

Curl debug features do not require compiling with C debug options. This
also made enabling debug features unintuitive and complicated to use.
Due to other issues (subject to PR #13694) it also caused an error in
default (and `Release`/`MinSizeRel`/`RelWithDebInfo`) configs, when
building the `testdeps` target:
```
ld: CMakeFiles/unit1395.dir/unit1395.c.o: in function `test':
unit1395.c:(.text+0x1a0): undefined reference to `dedotdotify'
```
Ref: https://github.com/curl/curl/actions/runs/9037287098/job/24835990826#step:3:2483

Fix it by always defining `DEBUGBUILD` when setting `ENABLE_DEBUG=ON`.
Decoupling this option from the selected CMake configuration.

Note that after this patch `ENABLE_DEBUG=ON` unconditionally enables
curl debug features. These features are insecure and unsuited for
production. Make sure to omit this option when building for production
in default, `Release` (and other not-`Debug`) modes.

Also delete a workaround no longer necessary in GHA CI jobs.

Ref: 1a62b6e (2015-03-03)
Ref: #13583
Closes #13592

Before this patch, building unit tests (= the `testdeps` target)
required `-DCURLDEBUG` be set either via `ENABLE_DEBUG=ON`
or `ENABLE_CURLDEBUG=ON`.

After fixing the build issues in curl#13694, the above requirement is no
longer necessary as a workaround. This patch makes unit tests build
unconditionally.

Depends-on: curl#13694 (fix build issues)
Depends-on: curl#13697 (fix unit test issue revealed by Old Linux CI job)
Follow-up to 39e7c22 curl#11446
Closes curl#13698

Before this patch, the `testdeps` build target required `-DCURLDEBUG`
be set either via `ENABLE_DEBUG=ON` or `ENABLE_CURLDEBUG=ON` to build
the curl unit tests.

After fixing build issues in #13694, we can drop this requirement and
build unit tests unconditionally.

Depends-on: #13694
Depends-on: #13697 (fix unit test issue revealed by Old Linux CI job)
Follow-up to 39e7c22 #11446
Closes #13698

…uilds

It affected cmake-unity shared-curltool curldebug mingw-w64 gcc builds
when building the `testdeps` target.

Apply the solution already used in `lib/base64.c` and `lib/dynbuf.c`
to fix it.

Also update an existing GHA CI job to test the issue fixed.

```
In file included from curl/lib/version_win32.c:35,
                 from curl/_bld/src/CMakeFiles/curl.dir/Unity/unity_0_c.c:145:
curl/lib/memdebug.h:52:14: error: redundant redeclaration of 'curl_dbg_logfile' [-Werror=redundant-decls]
   52 | extern FILE *curl_dbg_logfile;
      |              ^~~~~~~~~~~~~~~~
In file included from curl/src/slist_wc.c:32,
                 from curl/_bld/src/CMakeFiles/curl.dir/Unity/unity_0_c.c:4:
curl/lib/memdebug.h:52:14: note: previous declaration of 'curl_dbg_logfile' with type 'FILE *' {aka 'struct _iobuf *'}
   52 | extern FILE *curl_dbg_logfile;
      |              ^~~~~~~~~~~~~~~~
curl/lib/memdebug.h:55:44: error: redundant redeclaration of 'curl_dbg_malloc' [-Werror=redundant-decls]
   55 | CURL_EXTERN ALLOC_FUNC ALLOC_SIZE(1) void *curl_dbg_malloc(size_t size,
      |                                            ^~~~~~~~~~~~~~~
curl/lib/memdebug.h:55:44: note: previous declaration of 'curl_dbg_malloc' with type 'void *(size_t,  int,  const char *)' {aka 'void *(long long unsigned int,  int,  const char *)'}
   55 | CURL_EXTERN ALLOC_FUNC ALLOC_SIZE(1) void *curl_dbg_malloc(size_t size,
      |                                            ^~~~~~~~~~~~~~~
[...]
curl/lib/memdebug.h:110:17: error: redundant redeclaration of 'curl_dbg_fclose' [-Werror=redundant-decls]
  110 | CURL_EXTERN int curl_dbg_fclose(FILE *file, int line, const char *source);
      |                 ^~~~~~~~~~~~~~~
curl/lib/memdebug.h:110:17: note: previous declaration of 'curl_dbg_fclose' with type 'int(FILE *, int,  const char *)' {aka 'int(struct _iobuf *, int,  const char *)'}
  110 | CURL_EXTERN int curl_dbg_fclose(FILE *file, int line, const char *source);
      |                 ^~~~~~~~~~~~~~~
```
Ref: https://ci.appveyor.com/project/curlorg/curl/builds/49840554/job/a4aoet17e9qnqx1a#L362

After: https://ci.appveyor.com/project/curlorg/curl/builds/49843735/job/hbo2uah2vj0ns523

Ref: #13689 (CI testing this PR with `DEBUGBUILD`/`CURLDEBUG`/shared-static combinations)
Depends-on: #13694
Depends-on: #13800
Closes #13705

Follow-up to fc8e0de #13694

`CURLDEBUG` is meant to enable memory tracking, but in a bunch of cases,
it was protecting debug features that were supposed to be guarded with
`DEBUGBUILD`.

Replace these uses with `DEBUGBUILD`.

This leaves `CURLDEBUG` uses solely for its intended  purpose: to enable
the memory tracking debug feature.

Also:
- autotools: rely on `DEBUGBUILD` to enable `checksrc`.
  Instead of `CURLDEBUG`, which worked in most cases because debug
  builds enable `CURLDEBUG` by default, but it's not accurate.
- include `lib/easyif.h` instead of keeping a copy of a declaration.
- add CI test jobs for the build issues discovered.

Ref: #13694 (comment)
Closes #13718

Before this patch, autotools disabled building unit tests for
non-debug-enabled (`DEBUGBUILD`) builds. runtests skipped running this
combination, though they were built in cmake builds. There seems to be
no technical reason anymore for these restrictions. This patch removes
them, allowing to build and run unit tests for non-debug-enabled builds.

To improve unit test build and run coverage.

- autotools: do not disable building unit tests for non-debug-enabled
  build. Bringing behavior closer to cmake builds. (There are still
  exceptions in autotools, something for another PR)

- runtests: run unit tests for non-debug-enabled builds.
  It extends coverage by 50 tests.

- `lib/altsvc.c`: fix to include `CURL_TIME` support in libcurlu, for
  unit tests. It fixes test 1654, and syncs `CURL_TIME` behavior with
  test 1660 and `lib/hsts.c`.

Ref: 10a7d05
Ref: fc8e0de #13694
Ref: 99f78cb #16770

Closes #16771

Before this patch, autotools disabled building unit tests for
non-debug-enabled (`DEBUGBUILD`) builds. runtests skipped running this
combination, though they were built in cmake builds. There seems to be
no technical reason anymore for these restrictions. This patch removes
them, allowing to build and run unit tests for non-debug-enabled builds.

To improve unit test build and run coverage.

- autotools: do not disable building unit tests for non-debug-enabled
  build. Bringing behavior closer to cmake builds. (There are still
  exceptions in autotools, something for another PR)

- runtests: run unit tests for non-debug-enabled builds.
  It extends coverage by 50 tests.

- `lib/altsvc.c`: fix to include `CURL_TIME` support in libcurlu, for
  unit tests. It fixes test 1654, and syncs `CURL_TIME` behavior with
  test 1660 and `lib/hsts.c`.

Ref: 10a7d05
Ref: fc8e0de curl#13694
Ref: 99f78cb curl#16770

Closes curl#16771