Harden the "hardened" flags even more to comply with RHEL8 security rules

--- mariadb-10.3.10/CMakeLists.txt	2018-10-02 11:45:39.000000000 +0200
+++ mariadb-10.3.10/CMakeLists.txt_patched	2018-11-08 03:48:01.713969313 +0100
@@ -226,7 +226,7 @@ IF(NOT WITH_TSAN)
     # security-enhancing flags
     MY_CHECK_AND_SET_COMPILER_FLAG("-pie -fPIC")
     MY_CHECK_AND_SET_COMPILER_FLAG("-Wl,-z,relro,-z,now")
-    MY_CHECK_AND_SET_COMPILER_FLAG("-fstack-protector --param=ssp-buffer-size=4")
+    MY_CHECK_AND_SET_COMPILER_FLAG("-fstack-protector-strong --param=ssp-buffer-size=4")
     MY_CHECK_AND_SET_COMPILER_FLAG("-D_FORTIFY_SOURCE=2" RELEASE RELWITHDEBINFO)
   ENDIF()
 ENDIF()