[lldb] Make SWIG an autodetected depenency

[JDevlieghere]

Summary

This patch makes SWIG itself an autodetected dependency. This allows us to look for SWIG once in a centralized place and makes it easier downstream to detect whether to use the static bindings: https://github.com/apple/llvm-project/pull/5636

lldb/cmake/modules/FindLuaAndSwig.cmake

 #.rst:
 # FindLuaAndSwig
 # --------------
 #
 # Find Lua and SWIG as a whole.
 
 if(LUA_LIBRARIES AND LUA_INCLUDE_DIR AND SWIG_EXECUTABLE)
   set(LUAANDSWIG_FOUND TRUE)
 else()
-  find_package(SWIG 3.0)
-  if (SWIG_FOUND)
+  if (LLDB_ENABLE_SWIG)
     find_package(Lua 5.3 EXACT)
     if(LUA_FOUND AND SWIG_FOUND)
       mark_as_advanced(
         LUA_LIBRARIES
         LUA_INCLUDE_DIR
         SWIG_EXECUTABLE)
     endif()
   else()
     message(STATUS "SWIG 3 or later is required for Lua support in LLDB but could not be found")
   endif()
 
+
   include(FindPackageHandleStandardArgs)
   find_package_handle_standard_args(LuaAndSwig
                                     FOUND_VAR
                                       LUAANDSWIG_FOUND
                                     REQUIRED_VARS
                                       LUA_LIBRARIES
                                       LUA_INCLUDE_DIR
-                                      SWIG_EXECUTABLE)
+                                      LLDB_ENABLE_SWIG)
 endif()

lldb/cmake/modules/FindPythonAndSwig.cmake

mark_as_advanced(
       Python3_RPATH
       SWIG_EXECUTABLE)
   endif()
 endmacro()
 
 if(Python3_LIBRARIES AND Python3_INCLUDE_DIRS AND Python3_EXECUTABLE AND SWIG_EXECUTABLE)
   set(PYTHONANDSWIG_FOUND TRUE)
 else()
-  find_package(SWIG 3.0)
-  if (SWIG_FOUND)
-      FindPython3()
+  if (LLDB_ENABLE_SWIG)
   else()
     message(STATUS "SWIG 3 or later is required for Python support in LLDB but could not be found")
   endif()
 
   get_property(MULTI_CONFIG GLOBAL PROPERTY GENERATOR_IS_MULTI_CONFIG)
   if ("${Python3_VERSION}" VERSION_GREATER_EQUAL "3.7" AND
       "${SWIG_VERSION}" VERSION_LESS "4.0" AND WIN32 AND (
       ${MULTI_CONFIG} OR (uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")))
     # Technically this can happen with non-Windows builds too, but we are not
     # able to detect whether Python was built with assertions, and only Windows
     # has the requirement that Debug LLDB must use Debug Python.
     message(WARNING "Debug builds of LLDB are likely to be unusable due to "
       "<https://github.com/swig/swig/issues/1321>. Please use SWIG >= 4.0.")
   endif()
 
   include(FindPackageHandleStandardArgs)
   find_package_handle_standard_args(PythonAndSwig
                                     FOUND_VAR
                                       PYTHONANDSWIG_FOUND
                                     REQUIRED_VARS
                                       Python3_LIBRARIES
                                       Python3_INCLUDE_DIRS
                                       Python3_EXECUTABLE
-                                      SWIG_EXECUTABLE)
+                                      LLDB_ENABLE_SWIG)
 endif()

lldb/cmake/modules/LLDBConfig.cmake

if(${find_package})
     endif()
     find_package(${package} ${ARG_VERSION} ${maybe_required} ${maybe_quiet})
     set(${variable} "${${found}}")
   endif()
 
   message(STATUS "${description}: ${${variable}}")
 endmacro()
 
+add_optional_dependency(LLDB_ENABLE_SWIG "Enable SWIG to generate LLDB bindings" SWIG SWIG_FOUND VERSION 3)
 add_optional_dependency(LLDB_ENABLE_LIBEDIT "Enable editline support in LLDB" LibEdit LibEdit_FOUND)
 add_optional_dependency(LLDB_ENABLE_CURSES "Enable curses support in LLDB" CursesAndPanel CURSESANDPANEL_FOUND)
 add_optional_dependency(LLDB_ENABLE_LZMA "Enable LZMA compression support in LLDB" LibLZMA LIBLZMA_FOUND)
 add_optional_dependency(LLDB_ENABLE_LUA "Enable Lua scripting support in LLDB" LuaAndSwig LUAANDSWIG_FOUND)
 add_optional_dependency(LLDB_ENABLE_PYTHON "Enable Python scripting support in LLDB" PythonAndSwig PYTHONANDSWIG_FOUND)
 add_optional_dependency(LLDB_ENABLE_LIBXML2 "Enable Libxml 2 support in LLDB" LibXml2 LIBXML2_FOUND VERSION 2.8)
 add_optional_dependency(LLDB_ENABLE_FBSDVMCORE "Enable libfbsdvmcore support in LLDB" FBSDVMCore FBSDVMCore_FOUND QUIET)