Tests: Avoid cross-device links in CREATE_LINK test

Add a test for COPY_ON_ERROR to cover that scenario.

Tests/RunCMake/file/CREATE_LINK-COPY_ON_ERROR.cmake

@@ -0,0 +1,11 @@
+# Use COPY_ON_ERROR to handle the case where the source and destination
+# directory are on different devices. Cross-device links are not permitted
+# and the following command falls back to copying the file if link fails.
+file(CREATE_LINK
+  ${CMAKE_CURRENT_LIST_FILE} TestCreateLink.cmake
+  RESULT result
+  COPY_ON_ERROR
+  )
+if(NOT result STREQUAL "0")
+  message(SEND_ERROR "COPY_ON_ERROR failed: '${result}'")
+endif()

Tests/RunCMake/file/CREATE_LINK.cmake

@@ -1,4 +1,11 @@
-file(CREATE_LINK ${CMAKE_CURRENT_LIST_FILE} TestLink.cmake RESULT result)
+# start with a file in the same directory to avoid cross-device links
+set(test_file ${CMAKE_CURRENT_BINARY_DIR}/CreateLinkTest.txt)
+file(TOUCH ${test_file})
+
+file(CREATE_LINK
+  ${test_file} ${CMAKE_CURRENT_BINARY_DIR}/TestCreateLink.txt
+  RESULT result
+  )
 if(NOT result STREQUAL "0")
   message(SEND_ERROR "Hard link result='${result}'")
 endif()

Tests/RunCMake/file/RunCMakeTest.cmake

@@ -1,6 +1,7 @@
 include(RunCMake)
 
 run_cmake(CREATE_LINK)
+run_cmake(CREATE_LINK-COPY_ON_ERROR)
 run_cmake(CREATE_LINK-noarg)
 run_cmake(CREATE_LINK-noexist)
 run_cmake(DOWNLOAD-hash-mismatch)