Tests: Add test for 'cmake -E tar --mtime' option

Add a test for ensuring the `--mtime` option works as expected.

Tests/RunCMake/CommandLineTar/RunCMakeTest.cmake

@@ -34,3 +34,6 @@ run_cmake(zip)
 
 # Extracting only selected files or directories
 run_cmake(zip-filtered)
+
+# Use the --mtime option to set the mtime when creating archive
+run_cmake(set-mtime)

Tests/RunCMake/CommandLineTar/mtime-tests.cmake

@@ -0,0 +1,9 @@
+set(OUTPUT_NAME "test.tar")
+
+set(ARCHIVE_MTIME "1970-01-01UTC")
+set(ARCHIVE_MTIME_RFC3339 "1970-01-01T00:00:00Z")
+
+set(COMPRESSION_FLAGS cvf)
+set(COMPRESSION_OPTIONS --mtime=${ARCHIVE_MTIME})
+
+set(DECOMPRESSION_FLAGS xvf)

Tests/RunCMake/CommandLineTar/set-mtime.cmake

@@ -0,0 +1,11 @@
+include(${CMAKE_CURRENT_LIST_DIR}/mtime-tests.cmake)
+
+include(${CMAKE_CURRENT_LIST_DIR}/roundtrip.cmake)
+
+foreach(file ${CHECK_FILES})
+  file(TIMESTAMP ${FULL_DECOMPRESS_DIR}/${COMPRESS_DIR}/${file} MTIME UTC)
+  if(NOT MTIME STREQUAL ARCHIVE_MTIME_RFC3339)
+    message(FATAL_ERROR
+      "Extracted timestamp ${MTIME} does not match expected ${ARCHIVE_MTIME_RFC3339}")
+  endif()
+endforeach()