[lldb][CMake] Avoid 'Autogenerate scheme' dialogs in Xcode projects

Summary:
Supported in CMake 3.9 and higher: https://cmake.org/cmake/help/v3.9/variable/CMAKE_XCODE_GENERATE_SCHEME.html
Older versions will just report it as unused in the end of the configuration process.

Reviewers: jingham, JDevlieghere

Reviewed By: JDevlieghere

Subscribers: mgorny, lldb-commits, #lldb

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D65509

llvm-svn: 367538

lldb/cmake/caches/Apple-lldb-Xcode.cmake

@@ -2,3 +2,4 @@ include(${CMAKE_CURRENT_LIST_DIR}/Apple-lldb-base.cmake)
 
 set(LLDB_BUILD_FRAMEWORK ON CACHE BOOL "")
 set(CMAKE_OSX_DEPLOYMENT_TARGET 10.11 CACHE STRING "")
+set(CMAKE_XCODE_GENERATE_SCHEME ON CACHE BOOL "")