cmake: do not use CMP0074 unless it is supported

CMake CMP0074 was introduced by CMake 3.12, but we only require CMake
v3.10.2. so default to check `Boost_ROOT` unless specified otherwise.

Signed-off-by: Kefu Chai <kchai@redhat.com>

diff --git a/cmake/modules/FindBoost.cmake b/cmake/modules/FindBoost.cmake
index ebe18e3bc58ae5def0f31890bc056e6493610438..f96b2056bbd505baa74f711793d4999f6c11fc5c 100644 (file)
--- a/cmake/modules/FindBoost.cmake
+++ b/cmake/modules/FindBoost.cmake
@@ -1492,11 +1492,15 @@ if(WIN32)
     INTERFACE_COMPILE_DEFINITIONS "BOOST_ALL_NO_LIB")
 endif()
 
-cmake_policy(GET CMP0074 _Boost_CMP0074)
-if(NOT "x${_Boost_CMP0074}x" STREQUAL "xNEWx")
+if(POLICY CMP0074)
+  cmake_policy(GET CMP0074 _Boost_CMP0074)
+  if(NOT "x${_Boost_CMP0074}x" STREQUAL "xNEWx")
+    _Boost_CHECK_SPELLING(Boost_ROOT)
+  endif()
+  unset(_Boost_CMP0074)
+else()
   _Boost_CHECK_SPELLING(Boost_ROOT)
 endif()
-unset(_Boost_CMP0074)
 _Boost_CHECK_SPELLING(Boost_LIBRARYDIR)
 _Boost_CHECK_SPELLING(Boost_INCLUDEDIR)