Improve configure ODBC handling

configure.in

@@ -402,14 +402,16 @@ AM_CONDITIONAL([ENABLE_ZRTP],[test "x$enable_zrtp" != "xno"])
 
 AM_CONDITIONAL([WANT_DEBUG],[test "${enable_debug}" = "yes"])
 
+enable_core_odbc_support="no"
 AC_ARG_ENABLE(core-odbc-support,     
 	[AS_HELP_STRING([--enable-core-odbc-support], [Compile with ODBC Support])],,[enable_core_odbc_support="no"])
-AX_LIB_ODBC
-if test "$ac_cv_found_odbc" = "yes" ; then
-  enable_core_odbc_support="yes"
-fi
 if test "x$enable_core_odbc_support" != "xno"; then
-  AC_CHECK_LIB([odbc], [SQLDisconnect],, AC_MSG_ERROR([no usable libodbc; please install unixodbc devel package or equivalent]))
+  AX_LIB_ODBC
+  if test "x$ac_cv_found_odbc" = "xyes" ; then
+    enable_core_odbc_support="yes"
+  elif test "x$enable_core_odbc_support" = "xyes" ; then
+    AC_MSG_ERROR([no usable libodbc; please install unixodbc devel package or equivalent])
+  fi
 fi
 
 CHECK_LIBUUID