add framework path to link test to fix OS X SDK problem

Author: kyngchaos

cmake/FindOSGEARTH.cmake

@@ -105,6 +105,10 @@ IF( OSGEARTH_LIBRARY AND OSGEARTH_INCLUDE_DIR )
     SET(SAFE_CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES})
     SET(CMAKE_REQUIRED_INCLUDES ${CMAKE_REQUIRED_INCLUDES} ${OSGEARTH_INCLUDE_DIR})
     SET(CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES} ${OSGEARTHUTIL_LIBRARY})
+    IF(APPLE)
+        # no extra LDFLAGS used in link test, may fail in OS X SDK
+        SET(CMAKE_REQUIRED_LIBRARIES "-F/Library/Frameworks" ${CMAKE_REQUIRED_LIBRARIES})
+    ENDIF(APPLE)
     CHECK_CXX_SOURCE_COMPILES("
 #include <osgEarthUtil/Controls>
 using namespace osgEarth::Util::Controls;