Gate all xcselect checks behind CLANG_USE_XCSELECT

Author: carlocab

clang/CMakeLists.txt

@@ -214,30 +214,35 @@ if(GCC_INSTALL_PREFIX AND NOT USE_DEPRECATED_GCC_INSTALL_PREFIX)
     "See https://github.com/llvm/llvm-project/pull/77537 for detail.")
 endif()
 
-if(APPLE)
+cmake_dependent_option(CLANG_USE_XCSELECT "Use libxcselect to find the macOS SDK." OFF "APPLE" OFF)
+
+if(CLANG_USE_XCSELECT)
+  if(DEFAULT_SYSROOT)
+    message(FATAL_ERROR "Setting DEFAULT_SYSROOT is incompatible with CLANG_USE_XCSELECT.")
+  endif()
+
   check_include_file(xcselect.h CLANG_HAVE_XCSELECT_H)
-  if(CLANG_HAVE_XCSELECT_H)
-    include(CheckSymbolExists)
-    list(APPEND CMAKE_REQUIRED_LIBRARIES xcselect)
-    check_symbol_exists(xcselect_host_sdk_path xcselect.h CLANG_HAVE_XCSELECT_HOST_SDK_PATH)
-    list(REMOVE_ITEM CMAKE_REQUIRED_LIBRARIES xcselect)
+  if(NOT CLANG_HAVE_XCSELECT_H)
+    message(FATAL_ERROR "CLANG_USE_XCSELECT is enabled but xcselect.h was not found.")
   endif()
-endif()
 
-cmake_dependent_option(CLANG_USE_XCSELECT "Use libxcselect to find the macOS SDK." OFF
-  "APPLE;CLANG_HAVE_XCSELECT_HOST_SDK_PATH" OFF)
+  include(CheckSymbolExists)
+  list(APPEND CMAKE_REQUIRED_LIBRARIES xcselect)
+  check_symbol_exists(xcselect_host_sdk_path xcselect.h CLANG_HAVE_XCSELECT_HOST_SDK_PATH)
+  list(REMOVE_ITEM CMAKE_REQUIRED_LIBRARIES xcselect)
 
-if(DEFAULT_SYSROOT AND CLANG_USE_XCSELECT)
-  message(FATAL_ERROR "Setting DEFAULT_SYSROOT is incompatible with CLANG_USE_XCSELECT.")
-endif()
+  if(NOT CLANG_HAVE_XCSELECT_HOST_SDK_PATH)
+    message(FATAL_ERROR "CLANG_USE_XCSELECT is enabled but either libxcselect is not available "
+      "or it is missing xcselect_host_sdk_path.")
+  endif()
 
-if(CLANG_USE_XCSELECT)
   set(XCSELECT_VALID_POLICIES LATEST MATCHING_ONLY MATCHING_PREFERRED)
   set(CLANG_XCSELECT_HOST_SDK_POLICY "LATEST" CACHE STRING
     "Policy to use for xcselect. One of: ${XCSELECT_VALID_POLICIES}")
   set_property(CACHE CLANG_XCSELECT_HOST_SDK_POLICY PROPERTY STRINGS ${XCSELECT_VALID_POLICIES})
   string(TOUPPER ${CLANG_XCSELECT_HOST_SDK_POLICY} CLANG_XCSELECT_HOST_SDK_POLICY)
   list(JOIN XCSELECT_VALID_POLICIES "|" XCSELECT_POLICY_REGEX)
+
   if(NOT CLANG_XCSELECT_HOST_SDK_POLICY MATCHES "^XCSELECT_HOST_SDK_POLICY_(${XCSELECT_POLICY_REGEX})$")
     if(NOT CLANG_XCSELECT_HOST_SDK_POLICY IN_LIST XCSELECT_VALID_POLICIES)
       message(FATAL_ERROR