print deprecation warning when GTSAM_SLOW_BUT_CORRECT_EXPMAP is ON

Author: varunagrawal

cmake/HandleGeneralOptions.cmake

@@ -49,7 +49,9 @@ option(GTSAM_TANGENT_PREINTEGRATION         "Use new ImuFactor with integration
 option(GTSAM_SLOW_BUT_CORRECT_BETWEENFACTOR "Use the slower but correct version of BetweenFactor" OFF)
 option(GTSAM_SLOW_BUT_CORRECT_EXPMAP        "Use slower but correct expmap for Pose2"  ON)
 
-message(WARNING "GTSAM_SLOW_BUT_CORRECT_EXPMAP has been deprecated and will be removed in a future release.")
+if (GTSAM_SLOW_BUT_CORRECT_EXPMAP)
+    message(WARNING "GTSAM_SLOW_BUT_CORRECT_EXPMAP has been deprecated and will be removed in a future release.")
+endif()
 
 if (GTSAM_FORCE_SHARED_LIB AND GTSAM_FORCE_STATIC_LIB)
     message(FATAL_ERROR "GTSAM_FORCE_SHARED_LIB and GTSAM_FORCE_STATIC_LIB are both true. Please, to unambiguously select the desired library type to use to build GTSAM, set one of GTSAM_FORCE_SHARED_LIB=ON, GTSAM_FORCE_STATIC_LIB=ON, or BUILD_SHARED_LIBS={ON/OFF}")