Apple: Properly lookup XCTest for iOS and tvOS

Closes: #19172

Modules/FindXCTest.cmake

@@ -61,6 +61,22 @@ The following variables are set by including this module:
 
 #]=======================================================================]
 
+set(_PRESERVED_CMAKE_FIND_ROOT_PATH "${CMAKE_FIND_ROOT_PATH}")
+
+if(CMAKE_EFFECTIVE_SYSTEM_NAME STREQUAL "Apple"
+   AND NOT CMAKE_SYSTEM_NAME STREQUAL "Darwin")
+  # Non-macos systems set the CMAKE_FIND_ROOT_PATH_MODE to "ONLY" which
+  # restricts the search paths too much to find XCTest.framework. In
+  # contrast to the regular system frameworks which reside within the
+  # SDK direectory the XCTest framework is located in the respective
+  # platform directory which is not added to the CMAKE_FIND_ROOT_PATH
+  # (only to CMAKE_SYSTEM_FRAMEWORK_PATH) and therefore not searched.
+  #
+  # Until this is properly addressed, temporaily add the platform
+  # directory to CMAKE_FIND_ROOT_PATH.
+  list(APPEND CMAKE_FIND_ROOT_PATH "${_CMAKE_OSX_SYSROOT_PATH}/../..")
+endif()
+
 find_path(XCTest_INCLUDE_DIR
   NAMES "XCTest/XCTest.h"
   DOC "XCTest include directory")
@@ -71,6 +87,9 @@ find_library(XCTest_LIBRARY
   DOC "XCTest Framework library")
 mark_as_advanced(XCTest_LIBRARY)
 
+set(CMAKE_FIND_ROOT_PATH "${_PRESERVED_CMAKE_FIND_ROOT_PATH}")
+unset(_PRESERVED_CMAKE_FIND_ROOT_PATH)
+
 execute_process(
   COMMAND xcrun --find xctest
   OUTPUT_VARIABLE _xcrun_out OUTPUT_STRIP_TRAILING_WHITESPACE