Frontend: Add -experimental-skip-non-inlinable-function-bodies-is-lazy.

This option causes the -experimental-lazy-typecheck and
-experimental-skip-non-exportable-decls options to be inferred from the
presense of -experimental-skip-non-inlinable-function-bodies. This new option
is meant to be a temporary testing aid that allows lazy typechecking to be
tested on projects without full build system support for passing the other
flags to the right jobs.

Resolves rdar://118938251

lib/Frontend/CompilerInvocation.cpp

@@ -1503,6 +1503,9 @@ static bool ParseTypeCheckerArgs(TypeCheckerOptions &Opts, ArgList &Args,
   Opts.DebugGenericSignatures |= Args.hasArg(OPT_debug_generic_signatures);
 
   Opts.EnableLazyTypecheck |= Args.hasArg(OPT_experimental_lazy_typecheck);
+  Opts.EnableLazyTypecheck |=
+      Args.hasArg(OPT_experimental_skip_non_inlinable_function_bodies) &&
+      Args.hasArg(OPT_experimental_skip_non_inlinable_function_bodies_is_lazy);
 
   return HadError;
 }