Fix compiler check for stack unwind hint
Fix compiler check for stack unwind hint

The check inserts a DWARF directive to tell stack unwinding that the
bottom of the (co-routine) stack has been reached. Without this, stack
traces may attempt to continue past the bottom of the stack.

The GCC version check was incorrect, and failed to trigger for GCC
version 5.[0123].

flynn1973/mariadb-aix,flynn1973/mariadb-aix,ollie314/server,flynn1973/mariadb-aix,ollie314/server,flynn1973/mariadb-aix,ollie314/server,flynn1973/mariadb-aix,ollie314/server,flynn1973/mariadb-aix,flynn1973/mariadb-aix,natsys/mariadb_10.2,flynn1973/mariadb-aix,ollie314/server,natsys/mariadb_10.2,ollie314/server,flynn1973/mariadb-aix,flynn1973/mariadb-aix,ollie314/server,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,flynn1973/mariadb-aix,ollie314/server,natsys/mariadb_10.2,natsys/mariadb_10.2,ollie314/server,natsys/mariadb_10.2,natsys/mariadb_10.2,ollie314/server,slanterns/server,natsys/mariadb_10.2,ollie314/server,natsys/mariadb_10.2