AndroidTestUtilities: do not require ExternalData unconditionally

Attempting to use AndroidTestUtilities to simply install some local
files on device can result in the following error:

    Neither ExternalData_URL_TEMPLATES nor ExternalData_OBJECT_STORES is set

We no longer require these ExternalData-specific variables to be set if
no such remote data files are requested.

Fixes: #16529

Modules/AndroidTestUtilities.cmake

@@ -110,11 +110,18 @@ function(android_add_test_data test_name)
   endforeach()
 
   set(DATA_TARGET_NAME "${test_name}")
-  ExternalData_Expand_Arguments(
+  string(FIND "${AST_FILES}" "DATA{" data_files_found)
-    ${DATA_TARGET_NAME}
+  if(${data_files_found} GREATER "-1")
-    extern_data_output
+    # Use ExternalData if any DATA{} files were found.
-    ${AST_FILES})
+    ExternalData_Expand_Arguments(
-  ExternalData_Add_Target(${DATA_TARGET_NAME})
+      ${DATA_TARGET_NAME}
+      extern_data_output
+      ${AST_FILES})
+    ExternalData_Add_Target(${DATA_TARGET_NAME})
+  else()
+    add_custom_target(${DATA_TARGET_NAME} ALL)
+    set(extern_data_output ${AST_FILES})
+  endif()
 
   # For regular files on Linux, just copy them directly.
   foreach(path ${AST_FILES})

Tests/RunCMake/AndroidTestUtilities/RunCMakeTest.cmake

@@ -18,3 +18,4 @@ endfunction()
 run_ATU(SetupTest1 "")
 run_ATU(SetupTest2 "tests")
 run_ATU(SetupTest3 "tests")
+run_ATU(SetupTest4 "")

Tests/RunCMake/AndroidTestUtilities/SetupTest4.cmake

@@ -0,0 +1,13 @@
+enable_testing()
+include(AndroidTestUtilities)
+
+find_program(adb_executable adb)
+
+set(test_files "data/a.txt")
+
+set(ANDROID 1)
+
+android_add_test_data(setup_test
+  FILES ${test_files}
+  DEVICE_TEST_DIR "/data/local/tests/example1"
+  DEVICE_OBJECT_STORE "/sdcard/.ExternalData/SHA")

Tests/RunCMake/AndroidTestUtilities/SetupTest4Build-check.cmake

@@ -0,0 +1,5 @@
+include(${CMAKE_CURRENT_LIST_DIR}/check.cmake)
+compare_build_to_expected(FILES
+  "data/a.txt"
+  )
+check_for_setup_test()