sfm: Fix linking with gflags 2.2.2

gflags/gflags#259

Author: MehdiChinoune

modules/sfm/CMakeLists.txt

@@ -29,6 +29,8 @@ if(NOT DEFINED GFLAGS_INCLUDE_DIRS AND DEFINED GFLAGS_INCLUDE_DIR)
 endif()
 if(NOT GFLAGS_LIBRARIES AND TARGET gflags::gflags)
   set(GFLAGS_LIBRARIES gflags::gflags)
+elseif(NOT GFLAGS_LIBRARIES AND TARGET gflags)
+  set(GFLAGS_LIBRARIES gflags)
 endif()
 if(NOT DEFINED GLOG_INCLUDE_DIRS AND DEFINED GLOG_INCLUDE_DIR)
   set(GLOG_INCLUDE_DIRS "${GLOG_INCLUDE_DIR}")