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()