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

docs/INSTALL-CMAKE.md

@@ -246,7 +246,6 @@ target_link_libraries(my_target PRIVATE CURL::libcurl)
 - `CURL_STATIC_CRT`:                        Build libcurl with static CRT with MSVC (`/MT`) (requires UCRT, static libcurl or no curl executable). Default: `OFF`
 - `CURL_TARGET_WINDOWS_VERSION`:            Minimum target Windows version as hex string.
 - `CURL_WERROR`:                            Turn compiler warnings into errors. Default: `OFF`
-- `ENABLE_CURLDEBUG`:                       Enable TrackMemory debug feature. Default: =`ENABLE_DEBUG`
 - `ENABLE_CURL_MANUAL`:                     Build the man page for curl and enable its `-M`/`--manual` option. Default: `ON`
 - `ENABLE_DEBUG`:                           Enable curl debug features (for developing curl itself). Default: `OFF`
 - `IMPORT_LIB_SUFFIX`:                      Import library suffix. Default: `_imp` for MSVC-like toolchains, otherwise empty.
@@ -358,7 +357,7 @@ Details via CMake
 - `CURL_USE_GNUTLS`:                        Enable GnuTLS for SSL/TLS. Default: `OFF`
 - `CURL_USE_GSASL`:                         Use libgsasl. Default: `OFF`
 - `CURL_USE_GSSAPI`:                        Use GSSAPI implementation. Default: `OFF`
-- `CURL_USE_LIBBACKTRACE`:                  Use [libbacktrace](https://github.com/ianlancetaylor/libbacktrace). Requires build with TrackMemory and DWARF debug information. Default: `OFF`
+- `CURL_USE_LIBBACKTRACE`:                  Use [libbacktrace](https://github.com/ianlancetaylor/libbacktrace). Requires debug-enabled build and DWARF debug information. Default: `OFF`
 - `CURL_USE_LIBPSL`:                        Use libpsl. Default: `ON`
 - `CURL_USE_LIBSSH2`:                       Use libssh2. Default: `ON`
 - `CURL_USE_LIBSSH`:                        Use libssh. Default: `OFF`

docs/cmdline-opts/version.md

@@ -124,9 +124,6 @@ SSPI is supported.
 ## `TLS-SRP`
 SRP (Secure Remote Password) authentication is supported for TLS.
 
-## `TrackMemory`
-Debug memory tracking is supported.
-
 ## `Unicode`
 Unicode support on Windows.
 

docs/libcurl/curl_version_info.md

@@ -356,13 +356,6 @@ curl initialization. (Added in 7.84.0) See libcurl-thread(3)
 libcurl was built with support for TLS-SRP (in one or more of the built-in TLS
 backends).
 
-## `TrackMemory`
-
-*features* mask bit: CURL_VERSION_CURLDEBUG
-
-libcurl was built with memory tracking debug capabilities. This is mainly of
-interest for libcurl hackers.
-
 ## `Unicode`
 
 *features* mask bit: CURL_VERSION_UNICODE
@@ -391,6 +384,14 @@ callbacks. Always 0 since 7.82.0. Deprecated.
 
 ## no name
 
+*features* mask bit: CURL_VERSION_CURLDEBUG
+
+libcurl was built with memory tracking debug capabilities. This is mainly of
+interest for libcurl hackers. Always the same as CURL_VERSION_DEBUG since
+8.19.0. Deprecated.
+
+## no name
+
 *features* mask bit: CURL_VERSION_GSSNEGOTIATE
 
 supports HTTP GSS-Negotiate. Deprecated.

docs/libcurl/symbols-in-versions

@@ -161,7 +161,7 @@ CURL_VERSION_ASYNCHDNS          7.10.7
 CURL_VERSION_BITS               7.43.0
 CURL_VERSION_BROTLI             7.57.0
 CURL_VERSION_CONV               7.15.4
-CURL_VERSION_CURLDEBUG          7.19.6
+CURL_VERSION_CURLDEBUG          7.19.6        8.19.0
 CURL_VERSION_DEBUG              7.10.6
 CURL_VERSION_GSASL              7.76.0
 CURL_VERSION_GSSAPI             7.38.0

docs/tests/TEST-SUITE.md

@@ -175,7 +175,7 @@ SPDX-License-Identifier: curl
 ### Memory test
 
   The test script checks that all allocated memory is freed properly IF curl
-  has been built with the `CURLDEBUG` define set. The script automatically
+  has been built with the `DEBUGBUILD` define set. The script automatically
   detects if that is the case, and it uses the `memanalyze.pl` script to
   analyze the memory debugging output.