message: Only build lldb-tblgen if it's not a current target
  Summary:
  When doing standalone builds, you could potentially be building against
  an llvm which also built lldb. If this were the case, you'd be
  attempting to build this target twice.
  Reviewers: xiaobai
  Subscribers: mgorny
diff: +# tablegen targets get exported via llvm for LLVMConfig.cmake. So standalone
  +# builds of lldb can potentially import this via LLVMConfig and also attempt to
  +# build it in tree. So only build it if it doesn't exist.
  +if (TARGET lldb-tblgen)
  + set(LLDB_TABLEGEN_EXE $<TARGET_FILE:lldb-tblgen> CACHE STRING "")
  +else()
  set(LLVM_LINK_COMPONENTS Support)
  add_tablegen(lldb-tblgen LLDB
  @@ -5,4 +11,4 @@ add_tablegen(lldb-tblgen LLDB
  LLDBTableGen.cpp
  )
  set_target_properties(lldb-tblgen PROPERTIES FOLDER "LLDB tablegenning")
  -
  +endif()
  