cmake: do not introduce a policy stack in the package config

CMakeLists.txt

@@ -590,7 +590,7 @@ install (TARGETS glog
   LIBRARY DESTINATION ${_glog_CMake_LIBDIR}
   ARCHIVE DESTINATION ${_glog_CMake_LIBDIR})
 
-set (glog_POLICY_VERSION 3.0)
+set (glog_CMake_VERSION 3.0)
 
 if (gflags_FOUND)
   # Ensure clients locate only the package config and not third party find
@@ -600,7 +600,7 @@ if (gflags_FOUND)
   else (CMAKE_VERSION VERSION_LESS 3.9)
     # Passing additional find_package arguments to find_dependency is possible
     # starting with CMake 3.9.
-    set (glog_POLICY_VERSION 3.9)
+    set (glog_CMake_VERSION 3.9)
     set (gflags_DEPENDENCY "find_dependency (gflags ${gflags_VERSION} NO_MODULE)")
   endif (CMAKE_VERSION VERSION_LESS 3.9)
 endif (gflags_FOUND)

glog-config.cmake.in

-cmake_policy (PUSH)
-cmake_policy (VERSION @glog_POLICY_VERSION@)
+if (CMAKE_VERSION VERSION_LESS @glog_CMake_VERSION@)
+  message (FATAL_ERROR "CMake >= @glog_CMake_VERSION@ required")
+endif (CMAKE_VERSION VERSION_LESS @glog_CMake_VERSION@)
 
 @PACKAGE_INIT@
 
@@ -8,5 +9,3 @@ include (CMakeFindDependencyMacro)
 @gflags_DEPENDENCY@
 
 include ("${CMAKE_CURRENT_LIST_DIR}/glog-targets.cmake")
-
-cmake_policy (POP)