Added io_win32.h to header list in CMake config

This should fix #5717 and ensure that this header gets installed
properly on Windows.

cmake/extract_includes.bat.in

@@ -89,6 +89,7 @@ copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\casts.h" includ
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\common.h" include\google\protobuf\stubs\common.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\fastmem.h" include\google\protobuf\stubs\fastmem.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\hash.h" include\google\protobuf\stubs\hash.h
+copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\io_win32.h" include\google\protobuf\stubs\io_win32.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\logging.h" include\google\protobuf\stubs\logging.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\macros.h" include\google\protobuf\stubs\macros.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\mutex.h" include\google\protobuf\stubs\mutex.h