IRGen: internalize symbols with -static

This pipes the `-static` flag when building a static library into IRGen.
This should have no impact on non-Windows targets as the usage of the
information simply removes the `dllexport` attribute on the generated
interfaces.  This ensures that a library built with `-static` will not
re-export its interfaces from the consumer.  This is important to ensure
that the consumer does not vend the API surface when it statically links
a library.  In conjunction with the removal of the force load symbol,
this allows the generation of static libraries which may be linked
against on Windows.  However, a subsequent change is needed to ensure
that the consumer does not mark the symbol as being imported from a
foreign module (i.e. `dllimport`).

lib/Frontend/CompilerInvocation.cpp

@@ -2190,6 +2190,8 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
     Opts.InternalizeAtLink = true;
   }
 
+  Opts.InternalizeSymbols = FrontendOpts.Static;
+
   if (Args.hasArg(OPT_disable_preallocated_instantiation_caches)) {
     Opts.NoPreallocatedInstantiationCaches = true;
   }