[TEST-ONLY] Check swift generated PCM has correct dwo path

This is a testcase for rdar://156759645

Author: cachemeifyoucan

test/CAS/debug_info_pcm.swift

@@ -0,0 +1,43 @@
+// REQUIRES: OS=macosx
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -scan-dependencies -module-name Test -module-cache-path %t/clang-module-cache -O \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
+// RUN:   %t/test.swift -o %t/deps.json -cache-compile-job -cas-path %t/cas -I %t/include
+
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:SwiftShims > %t/shim.cmd
+// RUN: %swift_frontend_plain @%t/shim.cmd
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:B > %t/B.cmd
+// RUN: %swift_frontend_plain @%t/B.cmd
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:A > %t/A.cmd
+// RUN: %swift_frontend_plain @%t/A.cmd
+// RUN: %{python} %S/Inputs/SwiftDepsExtractor.py %t/deps.json clang:A modulePath > %t/A.path
+
+// RUN: dwarfdump --debug-info @%t/A.path | %FileCheck %s
+
+// CHECK: DW_AT_GNU_dwo_name
+// CHECK-SAME: BUILD_DIR
+
+//--- test.swift
+import A
+
+//--- include/a.h
+#include "b.h"
+struct A {
+  int a;
+};
+
+//--- include/b.h
+void b(void);
+
+//--- include/module.modulemap
+module A {
+  header "a.h"
+  export *
+}
+
+module B {
+  header "b.h"
+  export *
+}