Salsa-CI: Add MariaDB Connector C ABI version validation

The libmariadb3.symbols already checks that the ABI is stable in terms
of symbols/functions. Add extra test to ensure that the version functions
also continue to output expected strings. This helps avoid issues such
as the one happened in MariaDB 10.3.38/10.5.19 and for which upstream
still has submission open:
mariadb-corporation/mariadb-connector-c#219

Example output:
    $ g++ b1031863.cpp -l mariadb && ./a.out
    MARIADB_VERSION_ID: 30304
    MYSQL_VERSION_ID: 30304
    mysql_get_client_version(): 30304
    mysql_get_client_info(): 3.3.4

On failure it might say:

    ERROR: MARIADB_VERSION_ID started with 100338 instead of the expected 303!

debian/salsa-ci.yml

@@ -270,6 +270,36 @@ blhc:
     echo "Testing -l mariadbclient"
     g++ b933063.cpp -l mariadbclient && ./a.out | tee result
     if grep --quiet latin result; then echo "ERROR: Charset latin found!"; exit 1; fi
+  - |
+    # Build a test binary to verify API version strings
+    cat > b1031863.cpp <<EOF
+    #include <cstring>
+    #include <iostream>
+    #include <mysql/mysql.h>
+    using namespace std;
+
+    void test_if_starts_with(const string expected, const string tested, const string name) {
+      int r = strncmp(tested.c_str(), expected.c_str(), expected.size());
+      if (r == 0) {
+        cout << name << ": " << tested << "\n";
+      } else {
+        cout << "ERROR: " << name << " started with " << tested << " instead of the expected " << expected << "!\n";
+        exit(1);
+      }
+    }
+
+    int main()
+    {
+      MYSQL h;
+      test_if_starts_with("303", to_string(MARIADB_VERSION_ID), "MARIADB_VERSION_ID");
+      test_if_starts_with("303", to_string(MYSQL_VERSION_ID), "MYSQL_VERSION_ID");
+      test_if_starts_with("303", to_string(mysql_get_client_version()), "mysql_get_client_version()");
+      test_if_starts_with("3.3", mysql_get_client_info(), "mysql_get_client_info()");
+      return 0;
+    }
+    EOF
+    g++ b1031863.cpp -l mysqlclient && ./a.out
+
 
 fresh install:
   stage: test