Build: Use `string(APPEND…)` in the root `CMakeLists.txt`

CMakeLists.txt

@@ -420,10 +420,9 @@ if(NOT CMake_TEST_EXTERNAL_CMAKE)
       set(CMAKE_BUNDLE_LOCATION "${CMAKE_INSTALL_PREFIX}")
       # make sure CMAKE_INSTALL_PREFIX ends in /
       if(NOT CMAKE_INSTALL_PREFIX MATCHES "/$")
-        set(CMAKE_INSTALL_PREFIX "${CMAKE_INSTALL_PREFIX}/")
+        string(APPEND CMAKE_INSTALL_PREFIX "/")
       endif()
-      set(CMAKE_INSTALL_PREFIX
-        "${CMAKE_INSTALL_PREFIX}CMake.app/Contents")
+      string(APPEND CMAKE_INSTALL_PREFIX "CMake.app/Contents")
     endif()
   endif()
 
@@ -467,7 +466,7 @@ if(NOT CMake_TEST_EXTERNAL_CMAKE)
       foreach(FLAG_LANG IN ITEMS C CXX)
         foreach(FLAG IN LISTS ${FLAG_LANG}_FLAGS_LIST)
           if(NOT " ${CMAKE_${FLAG_LANG}_FLAGS} " MATCHES " ${FLAG} ")
-            set(CMAKE_${FLAG_LANG}_FLAGS "${CMAKE_${FLAG_LANG}_FLAGS} ${FLAG}")
+            string(APPEND CMAKE_${FLAG_LANG}_FLAGS " ${FLAG}")
           endif()
         endforeach()
       endforeach()