Add a way to add custom libraries to the mix. Also add status reporting

Modules/CheckVariableExists.cmake

@@ -8,15 +8,23 @@
 MACRO(CHECK_VARIABLE_EXISTS VAR VARIABLE)
   IF("${VARIABLE}" MATCHES "^${VARIABLE}$")
     SET(MACRO_CHECK_VARIABLE_DEFINITIONS -DCHECK_VARIABLE_EXISTS=${VAR})
+    MESSAGE(STATUS "Looking for ${VARIABLE}")
+    IF(CMAKE_REQUIRED_LIBRARIES)
+      SET(CHECK_VARIABLE_EXISTS_ADD_LIBRARIES 
+          "-DLINK_LIBRARIES:STRING=${CMAKE_REQUIRED_LIBRARIES}")
+    ENDIF(CMAKE_REQUIRED_LIBRARIES)
     TRY_COMPILE(${VARIABLE}
                ${CMAKE_BINARY_DIR}
                ${CMAKE_ROOT}/Modules/CheckVariableExists.c
                CMAKE_FLAGS -DCOMPILE_DEFINITIONS:STRING=${MACRO_CHECK_VARIABLE_DEFINITIONS}
+                        ${CHECK_VARIABLE_EXISTS_ADD_LIBRARIES}
                OUTPUT_VARIABLE OUTPUT)
     IF(${VARIABLE})
       SET(${VARIABLE} 1 CACHE INTERNAL "Have variable ${VAR}")
+      MESSAGE(STATUS "Looking for ${VARIABLE} - found")
     ELSE(${VARIABLE})
       SET(${VARIABLE} "" CACHE INTERNAL "Have variable ${VAR}")
+      MESSAGE(STATUS "Looking for ${VARIABLE} - not found")
       WRITE_FILE(${CMAKE_BINARY_DIR}/CMakeError.log 
         "Determining if the variable ${VAR} exists failed with the following output:\n"
         "${OUTPUT}\n" APPEND)