Merge branch 'feature/add_third_party_for_gflags' into feature/c_api

Author: reyoung

cmake/external/gflags.cmake

@@ -14,8 +14,8 @@
 
 INCLUDE(ExternalProject)
 
-SET(GFLAGS_SOURCES_DIR ${CMAKE_CURRENT_SOURCE_DIR}/third_party/gflags)
-SET(GFLAGS_INSTALL_DIR ${CMAKE_CURRENT_SOURCE_DIR}/third_party/install/gflags)
+SET(GFLAGS_SOURCES_DIR ${THIRD_PARTY_PATH}/gflags)
+SET(GFLAGS_INSTALL_DIR ${THIRD_PARTY_PATH}/install/gflags)
 SET(GFLAGS_INCLUDE_DIR "${GFLAGS_INSTALL_DIR}/include" CACHE PATH "gflags include directory." FORCE)
 IF(WIN32)
     set(GFLAGS_LIBRARIES "${GFLAGS_INSTALL_DIR}/lib/gflags.lib" CACHE FILEPATH "GFLAGS_LIBRARIES" FORCE)