libmariadbclient: fix missing zstd and curl in --libs_sys output

[thefallentree]

Problem

`CLIENT_PLUGIN_ZSTD=STATIC` and `CLIENT_PLUGIN_REMOTE_IO=STATIC` embed zstd
and curl code into `libmysqlclient_r.a`, but `mariadb_config --libs_sys` does
not report `-lzstd` or `-lcurl.dll`. This breaks static linking on Windows:
applications get undefined references to zstd symbols and `_imp_curl*` import
stubs at link time.

Repro (MINGW64/UCRT64, any project linking the static client lib):

```
libmysqlclient_r.a(compress_zstd.c.obj): undefined reference to `ZSTD_compress'
libmysqlclient_r.a(remote_io.c.obj): undefined reference to `__imp_curl_multi_init'
... (~25 more)
```

Root Cause

Both `ZSTD_LIBRARY` and `CURL_LIBRARIES` are appended to `SYSTEM_LIBS` inside
`libmariadb/CMakeLists.txt` without `PARENT_SCOPE`. The sibling
`mariadb_config/` subdirectory (processed after `libmariadb/`) reads the
top-level `SYSTEM_LIBS` to build the `@extra_dynamic_LDFLAGS@` substitution
that becomes `#define LIBS_SYS` in `mariadb_config.c`. It never sees those
additions, so `--libs_sys` only outputs the Win32 baseline
(`-lws2_32 -ladvapi32 ...`) and omits `-lzstd` and `-lcurl.dll`.

Fix

After `cmake` configure (which generates `mariadb_config.c`), patch that file
to append `-lzstd -lcurl.dll` to the `LIBS_SYS` string literal before it is
compiled into `mariadb_config.exe`.

`-lcurl.dll` (not `-lcurl`) is used deliberately: on MinGW the linker resolves
`-lcurl.dll` to `libcurl.dll.a` (the import library that provides the
`_imp_curl` stubs needed by the statically-embedded `remote_io` plugin),
whereas `-lcurl` may resolve to `libcurl.a` (the static archive, which does
not define `_imp_curl`).

[dragon-archer]

Usually a patch is better than a sed for this.

[thefallentree]

Usually a patch is better than a sed for this.

yeah this is unfortunately a bug in the upstream release, I am working on a patch instead