Fix linkage error in freebsd

src/CMakeLists.txt

@@ -224,11 +224,11 @@ ENDIF (WIN32)
 
 IF (WITH_CRASHHANDLER_GUI)
     LIST( APPEND VLMC_SRCS Gui/widgets/CrashHandler.cpp )
-    IF (UNIX)
+    IF ( CMAKE_SYSTEM_NAME STREQUAL "Linux" )
         LIST( APPEND VLMC_SRCS Tools/UnixBacktraceGenerator.cpp )
-    ELSEIF(WIN32)
+    ELSE ( CMAKE_SYSTEM_NAME STREQUAL "Linux" )
         LIST( APPEND VLMC_SRCS Tools/Win32BacktraceGenerator.cpp )
-    ENDIF(UNIX)
+    ENDIF( CMAKE_SYSTEM_NAME STREQUAL "Linux" )
     LIST( APPEND VLMC_HDRS Gui/widgets/CrashHandler.h Tools/BacktraceGenerator.h )
     LIST( APPEND VLMC_UIS Gui/widgets/CrashHandler.ui )