[LLDB] Fix standalone build with CMake 2.8.12.2, broken after adding SymbolFile PDB plugin

[Eugene.Zelenko]

Summary

LLVM and Clang CMakeLists.txt set this policy explicitly.

[zturner]

I think this should be in lldb/CMakeLists.txt, not in LLDBStandalone.cmake. What do you think?

[Eugene.Zelenko]

I didn't work in main CMakeLists.txt.

From other side, policy is not set only in standalone build, so place seems logical for me.

[zturner]

But in LLVM and clang as well, it's always set in top-level CMakeLists.txt
file, right? But you're saying for some reason that doesn't work in LLDB?

[Eugene.Zelenko]

My guess is that project() or cmake_minimum_required() resets policy value set in upper level make file.

[zturner]

Ahh that would make sense. I guess it needs to be set in both places in
that case?

[Eugene.Zelenko]

Probably not since in case of non-standalone build LLVM make file should be enough and LLDBStandalone.cmake will be not executed.

[zturner]

But it also has a project() and a cmake_required_version() statement, so if
that is what is causing the policy to be reset in LLDBStandalone, the same
would be true in that case too. Also clang CMakeLists.txt has it as the
top, and it's basically the same as LLDB

[Eugene.Zelenko]

Obsoleted by D20344.

cmake/modules/LLDBStandalone.cmake

   project(lldb)
   cmake_minimum_required(VERSION 2.8)
 
+  if (POLICY CMP0022)
+    cmake_policy(SET CMP0022 NEW) # automatic when 2.8.12 is required
+  endif()
+
   option(LLVM_INSTALL_TOOLCHAIN_ONLY "Only include toolchain files in the 'install' target." OFF)
 
   set(LLDB_PATH_TO_LLVM_SOURCE "" CACHE PATH