[debugserver,cmake] Add DEPENDS to custom commands.

[brucem]

Summary

Add dependencies to the custom commands so that they get
re-executed as needed.

tools/debugserver/source/MacOSX/CMakeLists.txt

 #add_subdirectory(arm64)
 #add_subdirectory(arm)
 add_subdirectory(i386)
 #add_subdirectory(ppc)
 add_subdirectory(x86_64)
 
 include_directories(..)
 
 set(generated_mach_interfaces
   ${CMAKE_CURRENT_BINARY_DIR}/mach_exc.h
   ${CMAKE_CURRENT_BINARY_DIR}/mach_excServer.c
   ${CMAKE_CURRENT_BINARY_DIR}/mach_excUser.c
   )
 add_custom_command(OUTPUT ${generated_mach_interfaces}
   COMMAND mig ${CMAKE_CURRENT_SOURCE_DIR}/dbgnub-mig.defs
+  DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/dbgnub-mig.defs
   )
 
 set(DEBUGSERVER_VERS_GENERATED_FILE ${CMAKE_CURRENT_BINARY_DIR}/debugserver_vers.c)
 set_source_files_properties(${DEBUGSERVER_VERS_GENERATED_FILE} PROPERTIES GENERATED 1)
 
 add_custom_command(OUTPUT ${DEBUGSERVER_VERS_GENERATED_FILE}
   COMMAND ${LLDB_SOURCE_DIR}/scripts/generate-vers.pl
           ${LLDB_SOURCE_DIR}/lldb.xcodeproj/project.pbxproj debugserver
-          > ${DEBUGSERVER_VERS_GENERATED_FILE})
+          > ${DEBUGSERVER_VERS_GENERATED_FILE}
+  DEPENDS ${LLDB_SOURCE_DIR}/scripts/generate-vers.pl
+          ${LLDB_SOURCE_DIR}/lldb.xcodeproj/project.pbxproj
+  )
 
 set(DEBUGSERVER_USED_LIBS
   lldbDebugserverCommon
   lldbUtility
   lldbDebugserverMacOSX_I386
   lldbDebugserverMacOSX_X86_64
   )