[modules] Add a comment to explain why -E leaves some #includes in the preprocessed output.

llvm-svn: 265766
diff --git a/clang/test/Modules/preprocess.cpp b/clang/test/Modules/preprocess.cpp
index aa28191..0615331 100644
--- a/clang/test/Modules/preprocess.cpp
+++ b/clang/test/Modules/preprocess.cpp
@@ -1,6 +1,6 @@
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs -x c++ -E %s | \
-// RUN:   FileCheck -strict-whitespace %s --check-prefix=CHECK --check-prefix=CXX
+// RUN:   FileCheck -strict-whitespace %s --check-prefix=CHECK --check-prefix=CXX --check-prefix=CXX-DASHE
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs -x objective-c -E %s | \
 // RUN:   FileCheck -strict-whitespace %s --check-prefix=CHECK --check-prefix=OBJC
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs -x c++ -E -frewrite-includes %s | \
@@ -14,7 +14,9 @@
 // The weird {{ }} here is to prevent the -frewrite-includes test from matching its own CHECK lines.
 
 // CXX: #include{{ }}"dummy.h"
+// CXX-DASHE-SAME: /* clang -E: implicit import for module dummy */
 // CXX: #include{{ }}"dummy.h"
+// CXX-DASHE-SAME: /* clang -E: implicit import for module dummy */
 // CXX: foo bar baz
 
 // OBJC: @import{{ }}dummy; /* clang