Xcode: Set CODE_SIGN_IDENTITY during compiler identification

If `CMAKE_XCODE_ATTRIBUTE_CODE_SIGN_IDENTITY` is set then propagate
it to the compiler id test project too.

Fixes: #18292

Modules/CMakeDetermineCompilerId.cmake

@@ -355,6 +355,12 @@ Id flags: ${testflags} ${CMAKE_${lang}_COMPILER_ID_FLAGS_ALWAYS}
     else()
       set(id_development_team "")
     endif()
+    if(DEFINED CMAKE_XCODE_ATTRIBUTE_CODE_SIGN_IDENTITY)
+      set(id_code_sign_identity
+        "CODE_SIGN_IDENTITY = \"${CMAKE_XCODE_ATTRIBUTE_CODE_SIGN_IDENTITY}\";")
+    else()
+      set(id_code_sign_identity "")
+    endif()
     configure_file(${CMAKE_ROOT}/Modules/CompilerId/Xcode-3.pbxproj.in
       ${id_dir}/CompilerId${lang}.xcodeproj/project.pbxproj @ONLY)
     unset(_ENV_MACOSX_DEPLOYMENT_TARGET)

Modules/CompilerId/Xcode-3.pbxproj.in

@@ -73,6 +73,7 @@
 			isa = XCBuildConfiguration;
 			buildSettings = {
 				@id_development_team@
+				@id_code_sign_identity@
 				PRODUCT_NAME = CompilerId@id_lang@;
 			};
 			name = Debug;