don't share MemberVariables module when testing diagnostics

This header is shared by 3 tests, one of which checks diagnostics. If
that test picks up an already built module from the module cache, it
won't pick up diagnostics in the header. This duplicates the header as
two separate modules rather than specifying an explicit module cache, to
avoid rebuilding CxxStdlib.

Author: hnrklssn

test/Interop/Cxx/class/Inputs/module.modulemap

@@ -48,7 +48,15 @@ module MemoryLayout {
   requires cplusplus
 }
 
-module MemberVariables {
+// This header is shared between 3 test cases. It's built with -verify in
+// test/Interop/Cxx/class/member-variables-typechecker.swift, which is defeated
+// if the test just picks up a cached module. We could set the module cache path
+// explicitly, but that would rebuild CxxStdlib which is really slow.
+module MemberVariablesNoDiagnostics {
+  header "member-variables.h"
+  requires cplusplus
+}
+module MemberVariablesDiagnostics {
   header "member-variables.h"
   requires cplusplus
 }

test/Interop/Cxx/class/member-variables-module-interface.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-ide-test -print-module -module-to-print=MemberVariables -I %S/Inputs -source-filename=x -enable-experimental-cxx-interop | %FileCheck %s
+// RUN: %target-swift-ide-test -print-module -module-to-print=MemberVariablesNoDiagnostics -I %S/Inputs -source-filename=x -enable-experimental-cxx-interop | %FileCheck %s
 
 // CHECK:      struct MyClass {
 // CHECK-NEXT:   init()

test/Interop/Cxx/class/member-variables-typechecker.swift

@@ -1,6 +1,6 @@
 // RUN: %target-typecheck-verify-swift -I %S/Inputs -enable-experimental-cxx-interop
 
-import MemberVariables
+import MemberVariablesDiagnostics
 
 var s = MyClass()
 s.const_member = 42 // expected-error {{cannot assign to property: 'const_member' setter is inaccessible}}

test/Interop/Cxx/class/zero-sized-field.swift

@@ -4,7 +4,7 @@
 // REQUIRES: executable_test
 
 import StdlibUnittest
-import MemberVariables
+import MemberVariablesNoDiagnostics
 
 var FieldsTestSuite = TestSuite("Generating code with zero sized fields")