(WIP) fix spurious exception spec error, PR38627

test/Modules/Inputs/lax-base-except/a.h

+class A {
+ public:
+  virtual ~A() = default;
+};
+
+class B {
+ public:
+  virtual ~B() {
+    c.func();
+  }
+
+  struct C{
+    void func() {}
+    friend B::~B();
+  };
+
+  C c;
+};

test/Modules/Inputs/lax-base-except/module.modulemap

+module a {
+  header "a.h"
+}

test/Modules/lax-base-except.cpp

+// RUN: rm -rf %t
+// RUN: %clang -c -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs/lax-base-except %s -o %t2.o
+// expected-no-diagnostics
+
+#include "a.h"
+
+class D : public A, public B {
+ public:
+  virtual ~D() override = default;
+};