Apple: Use include_guard() within compiler config

Modules/Platform/Apple-Clang.cmake

@@ -3,10 +3,7 @@
 
 
 # This module is shared by multiple languages; use include blocker.
-if(__APPLE_COMPILER_CLANG)
-  return()
-endif()
-set(__APPLE_COMPILER_CLANG 1)
+include_guard()
 
 macro(__apple_compiler_clang lang)
   set(CMAKE_${lang}_VERBOSE_FLAG "-v -Wl,-v") # also tell linker to print verbose output

Modules/Platform/Apple-GNU.cmake

@@ -3,10 +3,7 @@
 
 
 # This module is shared by multiple languages; use include blocker.
-if(__APPLE_COMPILER_GNU)
-  return()
-endif()
-set(__APPLE_COMPILER_GNU 1)
+include_guard()
 
 macro(__apple_compiler_gnu lang)
   set(CMAKE_${lang}_VERBOSE_FLAG "-v -Wl,-v") # also tell linker to print verbose output

Modules/Platform/Apple-Intel.cmake

@@ -3,10 +3,7 @@
 
 
 # This module is shared by multiple languages; use include blocker.
-if(__APPLE_COMPILER_INTEL)
-  return()
-endif()
-set(__APPLE_COMPILER_INTEL 1)
+include_guard()
 
 macro(__apple_compiler_intel lang)
   set(CMAKE_${lang}_VERBOSE_FLAG "-v -Wl,-v") # also tell linker to print verbose output

Modules/Platform/Apple-PGI.cmake

@@ -2,10 +2,7 @@
 # file Copyright.txt or https://cmake.org/licensing for details.
 
 # This module is shared by multiple languages; use include blocker.
-if(__APPLE_COMPILER_PGI)
-  return()
-endif()
-set(__APPLE_COMPILER_PGI 1)
+include_guard()
 
 macro(__apple_compiler_pgi lang)
   set(CMAKE_${lang}_OSX_COMPATIBILITY_VERSION_FLAG "-Wl,-compatibility_version,")