Merge pull request #1858 from Exiv2/mergify/bp/0.27-maintenance/pr-1857

Fix compiler warning on Apple/M1/Clang (backport #1857)

cmake/compilerFlags.cmake

@@ -23,9 +23,13 @@ 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))
-            check_cxx_compiler_flag(-fstack-clash-protection HAS_FSTACK_CLASH_PROTECTION)
+            # 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)
             check_cxx_compiler_flag(-fstack-protector-strong HAS_FSTACK_PROTECTOR_STRONG)
             if(HAS_FSTACK_CLASH_PROTECTION)