[lldb/CMake] Only auto-enable Python when SWIG is found

As correctly pointed out by Martin on the mailing list, Python should
only be auto-enabled if SWIG is found as well. This moves the logic of
finding SWIG into FindPythonInterpAndLibs to make that possible.

To make diagnosing easier I've included a status message to convey why
Python support is disabled.

lldb/scripts/CMakeLists.txt

@@ -15,12 +15,6 @@ if(LLDB_BUILD_FRAMEWORK)
   set(framework_arg --framework --target-platform Darwin)
 endif()
 
-find_package(SWIG REQUIRED)
-set(SWIG_MIN_VERSION "2.0.0")
-if (${SWIG_VERSION} VERSION_LESS ${SWIG_MIN_VERSION})
-  message(FATAL_ERROR "LLDB requires swig ${SWIG_MIN_VERSION}, your version is ${SWIG_VERSION}.")
-endif()
-
 if(APPLE)
   set(DARWIN_EXTRAS "-D__APPLE__")
 else()
@@ -38,7 +32,6 @@ set(SWIG_COMMON_FLAGS
   -outdir ${CMAKE_CURRENT_BINARY_DIR}
 )
 
-
 if (LLDB_ENABLE_PYTHON)
   add_custom_command(
     OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/LLDBWrapPython.cpp