[test] Add a test for indirect link dependencies relying on -L.

...as described in rdar://problem/23588774. We don't really have a good way
to make this test cross-platform as such, but I'll add a Linux version soon.

validation-test/execution/Inputs/custom-modules/foo.h

@@ -0,0 +1 @@
+int test();

validation-test/execution/Inputs/custom-modules/module.modulemap

@@ -0,0 +1,4 @@
+module foo {
+  header "foo.h"
+  link "foo"
+}

validation-test/execution/interpret-with-dependencies.swift

@@ -0,0 +1,16 @@
+// REQUIRES: OS=macosx
+// RUN: rm -rf %t && mkdir %t
+
+// RUN: echo 'int abc = 42;' | %clang -x c - -dynamiclib -Xlinker -install_name -Xlinker libabc.dylib -o %t/libabc.dylib
+// RUN: echo 'int test() { extern int abc; return abc; }' | %clang -x c - -L%t -dynamiclib -labc -o %t/libfoo.dylib
+
+// RUN: %swift_driver -I %S/Inputs/custom-modules -L%t %s | FileCheck %s
+// CHECK: {{okay}}
+
+import foo
+
+if test() == 42 {
+  print("okay")
+} else {
+  print("problem")
+}