cmake: test availability of -fcf-protection

Builds on an Orange Pi running Ubuntu 22.04 fail if -fcf-protection
is used.  Compilers are 11.4.0. Architecture is aarch64.

c++, g++ and gcc return: cc1plus:

    error: ‘-fcf-protection=full’ is not supported for this target

mythtv/external/libexiv2/cmake/compilerFlags.cmake

@@ -26,7 +26,11 @@ if ( MINGW OR UNIX OR MSYS ) # MINGW, Linux, APPLE, CYGWIN
         # This fails under Fedora - MinGW - Gcc 8.3
         if (NOT MINGW)
             if (COMPILER_IS_GCC AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 8.0)
-                add_compile_options(-fstack-clash-protection -fcf-protection)
+                add_compile_options(-fstack-clash-protection)
+                check_cxx_compiler_flag(-fcf-protection HAS_FCF_PROTECTION)
+                if (${HAS_FCF_PROTECTION})
+                    add_compile_options(-fcf-protection)
+                endif()
             endif()
 
             if (COMPILER_IS_GCC OR (COMPILER_IS_CLANG AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 3.7 ))