Hide all driver private symbols from runtime library

Use GCC visibility pragma to hide all driver private symbols which should
not be exported to other runtime libraries. This GCC visibility pragma is
supported since GCC 4.1.0.

All non-static functions and variables in C sources of DBD::MariaDB would
not be visible or exported to other runtime libraries.

This fixes problem when two or more DBI drivers (probably DBD::mysql)
export same function symbol as DBD::MariaDB. It could cause unexpected
behavior when more DBI drivers are used by Perl applications as correct
function symbol for driver does not have to be loaded.

Author: pali

dbdimp.c

@@ -15,6 +15,16 @@
 
 #include "dbdimp.h"
 
+#ifdef HAVE_GET_CHARSET_NUMBER
+/* Available only in some clients and declared in header file my_sys.h which cannot be included */
+unsigned int get_charset_number(const char *cs_name, unsigned int cs_flags);
+#endif
+
+#if defined(__GNUC__) && ((__GNUC__ == 4 && __GNUC_MINOR__ >= 1) || (__GNUC__ > 4))
+/* Do not export non-static functions from driver library */
+#pragma GCC visibility push(hidden)
+#endif
+
 #define ASYNC_CHECK_RETURN(h, value)\
   if(imp_dbh->async_query_in_flight) {\
       mariadb_dr_do_error(h, CR_UNKNOWN_ERROR, "Calling a synchronous function on an asynchronous handle", "HY000");\
@@ -1364,11 +1374,6 @@ static void error_no_connection(SV *h, const char *msg)
   mariadb_dr_do_error(h, CR_CONNECTION_ERROR, msg, "HY000");
 }
 
-#ifdef HAVE_GET_CHARSET_NUMBER
-/* Available only in some clients and declared in header file my_sys.h which cannot be included */
-unsigned int get_charset_number(const char *cs_name, unsigned int cs_flags);
-#endif
-
 /***************************************************************************
  *
  *  Name:    mariadb_dr_connect

socket.c

@@ -16,6 +16,11 @@
 #include <unistd.h>
 #endif
 
+#if defined(__GNUC__) && ((__GNUC__ == 4 && __GNUC_MINOR__ >= 1) || (__GNUC__ > 4))
+/* Do not export non-static functions from driver library */
+#pragma GCC visibility push(hidden)
+#endif
+
 /*
  * Warning: Native socket code must be outside of dbdimp.c and dbdimp.h because
  *          perl header files redefine socket function. This file must not