Reverts third_party/protobuf: Update to HEAD (f52e188fe4)

third_party/protobuf/cmake/protobuf-config.cmake.in

Index: third_party/protobuf/cmake/protobuf-config.cmake.in
diff --git a/third_party/protobuf/cmake/protobuf-config.cmake.in b/third_party/protobuf/cmake/protobuf-config.cmake.in
index a044fe5c676c4f246665b9e1a30c68507d547cc0..bb0997b88be7edc6c623af1a29128695ba5e0d43 100644
--- a/third_party/protobuf/cmake/protobuf-config.cmake.in
+++ b/third_party/protobuf/cmake/protobuf-config.cmake.in
@@ -1,13 +1,27 @@
-# User options
-include("${CMAKE_CURRENT_LIST_DIR}/protobuf-options.cmake")
+# Version info variables
+set(PROTOBUF_VERSION        "@protobuf_VERSION@")
+set(PROTOBUF_VERSION_STRING "@protobuf_VERSION_STRING@")
 
-# Depend packages
-@_protobuf_FIND_ZLIB@
+# Current dir
+get_filename_component(_PROTOBUF_PACKAGE_PREFIX
+  "${CMAKE_CURRENT_LIST_FILE}" PATH)
 
 # Imported targets
-include("${CMAKE_CURRENT_LIST_DIR}/protobuf-targets.cmake")
+include("${_PROTOBUF_PACKAGE_PREFIX}/protobuf-targets.cmake")
+
+# Compute the installation prefix relative to this file.
+get_filename_component(_PROTOBUF_IMPORT_PREFIX
+  "${_PROTOBUF_PACKAGE_PREFIX}" PATH)
+get_filename_component(_PROTOBUF_IMPORT_PREFIX
+  "${_PROTOBUF_IMPORT_PREFIX}" PATH)
+get_filename_component(_PROTOBUF_IMPORT_PREFIX
+  "${_PROTOBUF_IMPORT_PREFIX}" PATH)
 
 # CMake FindProtobuf module compatible file
-if(protobuf_MODULE_COMPATIBLE)
-  include("${CMAKE_CURRENT_LIST_DIR}/protobuf-module.cmake")
+if(NOT DEFINED PROTOBUF_MODULE_COMPATIBLE OR "${PROTOBUF_MODULE_COMPATIBLE}")
+  include("${_PROTOBUF_PACKAGE_PREFIX}/protobuf-module.cmake")
 endif()
+
+# Cleanup temporary variables.
+set(_PROTOBUF_PACKAGE_PREFIX)
+set(_PROTOBUF_IMPORT_PREFIX)