Merge pull request #1857 from kevinbackhouse/FixBuildAppleM1

Fix compiler warning on Apple/M1/Clang

cmake/compilerFlags.cmake

@@ -31,9 +31,11 @@ if ( MINGW OR UNIX OR MSYS ) # MINGW, Linux, APPLE, CYGWIN
 
 
     if (COMPILER_IS_GCC OR COMPILER_IS_CLANG)
-        # This fails under Fedora - MinGW - Gcc 8.3
+        # This fails under Fedora - MinGW - Gcc 8.3 and macOS/M1
         if (NOT (MINGW OR CYGWIN OR CMAKE_HOST_SOLARIS))
-            if (NOT APPLE) # Don't know why this isn't working correctly on Apple with M1 processor
+            # macOS M1 will set ARCHITECTURE == arm64
+            EXECUTE_PROCESS( COMMAND uname -m COMMAND tr -d '\n' OUTPUT_VARIABLE ARCHITECTURE )
+            if ( NOT ${ARCHITECTURE} STREQUAL arm64 )
                 check_cxx_compiler_flag(-fstack-clash-protection HAS_FSTACK_CLASH_PROTECTION)
             endif()
             check_cxx_compiler_flag(-fcf-protection HAS_FCF_PROTECTION)