Driver: Pass the new -sil-merge-partial-modules flag

Also pass flags to disable SIL optimization passes when merging
modules, since that's completely unnecessary.

An evolution test that used to fail with WMO disabled now passes
with this change.

FIxes <rdar://problem/18913977>.

Author: slavapestov

lib/Driver/ToolChains.cpp

@@ -687,6 +687,14 @@ ToolChain::constructInvocation(const MergeModuleJobAction &job,
   // serialized ASTs.
   Arguments.push_back("-parse-as-library");
 
+  // Merge serialized SIL from partial modules.
+  Arguments.push_back("-sil-merge-partial-modules");
+
+  // Disable SIL optimization passes; we've already optimized the code in each
+  // partial mode.
+  Arguments.push_back("-disable-diagnostic-passes");
+  Arguments.push_back("-disable-sil-perf-optzns");
+
   addCommonFrontendArgs(*this, context.OI, context.Output, context.Args,
                         Arguments);
   context.Args.AddLastArg(Arguments, options::OPT_import_objc_header);

validation-test/Evolution/test_function_change_transparent_body.swift

@@ -1,9 +1,6 @@
-// RUN: %target-resilience-test-wmo
+// RUN: %target-resilience-test
 // REQUIRES: executable_test
 
-// FIXME: shouldn't need -whole-module-optimization here; we need to fix the
-// frontend to merge serialized SIL functions from different translation units
-
 import StdlibUnittest
 import function_change_transparent_body