Tests/RunCMake/execute_process: Add test for ENCODING AUTO

On Windows the AUTO encoding is based on the console code page,
so run the test in an isolated console window.

Tests/RunCMake/execute_process/Encoding-common.cmake

@@ -0,0 +1,11 @@
+if(ENCODING)
+  set(maybe_ENCODING ENCODING ${ENCODING})
+else()
+  set(maybe_ENCODING "")
+  set(ENCODING AUTO) # execute_process's default ENCODING
+endif()
+execute_process(
+  COMMAND ${TEST_ENCODING_EXE} ${ENCODING} ${CMAKE_CURRENT_LIST_DIR}/Encoding${ENCODING}-stderr.txt
+  OUTPUT_VARIABLE out
+  ${maybe_ENCODING}
+  )

Tests/RunCMake/execute_process/Encoding-windows.cmake

@@ -0,0 +1,7 @@
+# Set the console code page.
+execute_process(COMMAND cmd /c chcp ${CODEPAGE})
+
+include(${CMAKE_CURRENT_LIST_DIR}/Encoding-common.cmake)
+
+# Save our internal UTF-8 representation of the output.
+file(WRITE "out.txt" "${out}")

Tests/RunCMake/execute_process/Encoding.cmake

@@ -1,6 +1,14 @@
-execute_process(
-  COMMAND ${TEST_ENCODING_EXE} ${ENCODING} ${CMAKE_CURRENT_LIST_DIR}/Encoding${ENCODING}-stderr.txt
-  OUTPUT_VARIABLE out
-  ENCODING ${ENCODING}
-  )
+if(CMAKE_HOST_WIN32 AND CODEPAGE)
+  # Run cmake in a new Window to isolate its console code page.
+  execute_process(COMMAND cmd /c start /min /wait ""
+    ${CMAKE_COMMAND} -DTEST_ENCODING_EXE=${TEST_ENCODING_EXE}
+                     -DENCODING=${ENCODING}
+                     -DCODEPAGE=${CODEPAGE}
+                     -P ${CMAKE_CURRENT_LIST_DIR}/Encoding-windows.cmake)
+
+  # Load our internal UTF-8 representation of the output.
+  file(READ "out.txt" out)
+else()
+  include(${CMAKE_CURRENT_LIST_DIR}/Encoding-common.cmake)
+endif()
 message("${out}")

Tests/RunCMake/execute_process/EncodingAUTO-stderr.txt

@@ -0,0 +1,2 @@
+Chinese
+注意

Tests/RunCMake/execute_process/EncodingAUTO.cmake

@@ -0,0 +1,3 @@
+set(ENCODING AUTO)
+set(CODEPAGE 54936)
+include(${CMAKE_CURRENT_LIST_DIR}/Encoding.cmake)

Tests/RunCMake/execute_process/RunCMakeTest.cmake

@@ -9,6 +9,7 @@ run_cmake_command(MergeOutputVars ${CMAKE_COMMAND} -P ${RunCMake_SOURCE_DIR}/Mer
 
 run_cmake(EncodingMissing)
 if(TEST_ENCODING_EXE)
+  run_cmake_script(EncodingAUTO -DTEST_ENCODING_EXE=${TEST_ENCODING_EXE})
   run_cmake_script(EncodingUTF-8 -DTEST_ENCODING_EXE=${TEST_ENCODING_EXE})
   run_cmake_script(EncodingUTF8 -DTEST_ENCODING_EXE=${TEST_ENCODING_EXE})
 endif()