message: Add back lldb-framework-headers target
  In r338058 we removed the target `lldb-framework-headers`, which mean
  lldb-framework no longer depended on `framework_headers`, so they never
  actually got generated. This is a partial revert of r338058: I added
  back the lldb-framework-headers target, but the framework-header-fix.sh
  script still runs on the copied headers.
diff: @@ -13,6 +13,8 @@ foreach(header
  list(APPEND framework_headers ${CMAKE_CURRENT_BINARY_DIR}/FrameworkHeaders/${basename})
  endforeach()
  +add_custom_target(lldb-framework-headers DEPENDS ${framework_headers})
  +
  add_custom_command(TARGET lldb-framework POST_BUILD
  COMMAND ${CMAKE_COMMAND} -E copy_directory ${CMAKE_CURRENT_BINARY_DIR}/FrameworkHeaders $<TARGET_FILE_DIR:liblldb>/Headers
  COMMAND ${LLDB_SOURCE_DIR}/scripts/framework-header-fix.sh $<TARGET_FILE_DIR:liblldb>/Headers ${LLDB_VERSION}
  @@ -38,4 +40,5 @@ set_target_properties(liblldb PROPERTIES
  PUBLIC_HEADER "${framework_headers}")
  add_dependencies(lldb-framework
  + lldb-framework-headers
  lldb-suite)
  