Double-quote file paths in extract_includes.bat.in

This allows the file path to contain spaces which is very common on
windows.

cmake/install.cmake

@@ -20,18 +20,12 @@ install(TARGETS protoc EXPORT protobuf-targets
 file(STRINGS extract_includes.bat.in _extract_strings
   REGEX "^copy")
 foreach(_extract_string ${_extract_strings})
-  string(REPLACE "copy \${PROTOBUF_SOURCE_WIN32_PATH}\\" ""
-    _extract_string ${_extract_string})
-  string(REPLACE "\\" "/" _extract_string ${_extract_string})
-  string(REGEX MATCH "^[^ ]+"
-    _extract_from ${_extract_string})
-  string(REGEX REPLACE "^${_extract_from} ([^$]+)" "\\1"
-    _extract_to ${_extract_string})
-  get_filename_component(_extract_from "${protobuf_SOURCE_DIR}/${_extract_from}" ABSOLUTE)
-  get_filename_component(_extract_name ${_extract_to} NAME)
-  get_filename_component(_extract_to ${_extract_to} PATH)
-  string(REPLACE "include/" "${CMAKE_INSTALL_INCLUDEDIR}/"
-    _extract_to "${_extract_to}")
+  string(REGEX REPLACE "^.* .+ include\\\\(.+)$" "\\1"
+    _header ${_extract_string})
+  string(REPLACE "\\" "/" _header ${_header})
+  get_filename_component(_extract_from "${protobuf_SOURCE_DIR}/../src/${_header}" ABSOLUTE)
+  get_filename_component(_extract_name ${_header} NAME)
+  get_filename_component(_extract_to "${CMAKE_INSTALL_INCLUDEDIR}/${_header}" PATH)
   if(EXISTS "${_extract_from}")
     install(FILES "${_extract_from}"
       DESTINATION "${_extract_to}"