build: merge TrackMemory (CURLDEBUG) into debug-enabled option

Drop separate `TrackMemory` (aka `CURLDEBUG`) debug feature.

After recent changes (thread-safety,
193cb00ce9, and updates leading up to
it), `TrackMemory` is unlikely to cause build or runtime issues.

To simplify builds and debug options, enable `TrackMemory`
unconditionally for debug-enabled (aka `DEBUGBUILD`) builds. Before
this patch, this was already the default, with an option to disable
it, or enable it in non-debug-enabled builds.

Note, in practice these two debug options already went hand in hand. It
was not possible to toggle them separately for a long time due to bugs,
before 59dc9f7e69 (2024-05-28) fixed it.

This patch also removes/deprecates separate knobs and feature flags for
`TrackMemory`:
- autotools: `--enable-curldebug`/`--disable-curldebug`
- cmake: `-DENABLE_CURLDEBUG=ON`/`OFF`
- C macro: `CURLDEBUG`
- libcurl: `CURL_VERSION_CURLDEBUG` symbol deprecated in favor
  of `CURL_VERSION_DEBUG`. They always return the same value after this
  patch.

Also:
- drop `TrackMemory` from `curl -V` output.
- rename internal `CURLDEBUG` macro to `CURL_MEMDEBUG` internally.
  To avoid confusion with `DEBUGBUILD`, but to keep guarding
  `TrackMemory`-related internals for readability.
- runtests: bind `TrackMemory` to debug feature. Keep it a separate
  test feature requirement, for clarity.
- CI: drop test builds for combinations of the two options.
- GHA/linux: no longer disable TrackMemory in the TSAN job.

Ref: https://github.com/curl/curl/pull/20328#issuecomment-3754528407

Closes #20331

src/Makefile.am

@@ -57,9 +57,6 @@ endif
 if DEBUGBUILD
 AM_CPPFLAGS += -DDEBUGBUILD
 endif
-if CURLDEBUG
-AM_CPPFLAGS += -DCURLDEBUG
-endif
 
 if USE_UNICODE
 UNICODEFLAG = -municode

src/curl.rc

@@ -32,7 +32,7 @@ VS_VERSION_INFO VERSIONINFO
   FILEVERSION     RC_VERSION
   PRODUCTVERSION  RC_VERSION
   FILEFLAGSMASK   VS_FFI_FILEFLAGSMASK
-#if defined(DEBUGBUILD) || defined(UNITTESTS) || defined(CURLDEBUG) || defined(_DEBUG)
+#if defined(DEBUGBUILD) || defined(UNITTESTS) || defined(_DEBUG)
   FILEFLAGS VS_FF_DEBUG
 #else
   FILEFLAGS 0L

src/curlinfo.c

@@ -234,7 +234,7 @@ static const char *disabled[] = {
 #endif
   ,
   "override-dns: "
-#if defined(CURLDEBUG) &&                                       \
+#if defined(CURL_MEMDEBUG) &&                              \
   (defined(CURLRES_ARES) || defined(USE_FAKE_GETADDRINFO))
   "ON"
 #else

src/tool_libinfo.c

@@ -114,7 +114,6 @@ static struct feature_name_presentp {
   { "SSLS-EXPORT",    &feature_ssls_export, 0 },
   { "threadsafe",     NULL,                 CURL_VERSION_THREADSAFE },
   { "TLS-SRP",        &feature_tls_srp,     CURL_VERSION_TLSAUTH_SRP },
-  { "TrackMemory",    NULL,                 CURL_VERSION_CURLDEBUG },
   { "Unicode",        NULL,                 CURL_VERSION_UNICODE },
   { "UnixSockets",    NULL,                 CURL_VERSION_UNIX_SOCKETS },
   { "zstd",           &feature_zstd,        CURL_VERSION_ZSTD },

src/tool_main.c

@@ -98,7 +98,7 @@ static int main_checkfds(void)
 #define main_checkfds() 0
 #endif
 
-#ifdef CURLDEBUG
+#ifdef CURL_MEMDEBUG
 static void memory_tracking_init(void)
 {
   char *env;