GCC compile option -mmitigate-rop is not supported in GCC version >= 9.1

[SpindlyKillerFish]

In CMakeLists.txt if compiler if GNUCC and C compilers version is greater that 6 then the compile option
-mmitigate-rop is added, but this throws an error with GCC compiler >= 9.1

[tomasbw]

Issue was resolved.