Add an integration test for debugging swiftpm products

<rdar://problem/55668148>

Author: aciidgh

test-lldb-with-c-package/CFoo/Package.swift

@@ -0,0 +1,11 @@
+// swift-tools-version:4.2
+import PackageDescription
+
+let package = Package(
+    name: "Foo",
+    targets: [
+        .target(name: "See"),
+        .target(name: "Core", dependencies: ["See"]),
+        .target(name: "exec", dependencies: ["Core"]),
+    ]
+)

test-lldb-with-c-package/CFoo/foo.c

@@ -0,0 +1,24 @@
+// Check that we can debug a Swift package.
+//
+// Make a sandbox dir.
+// RUN: rm -rf %t.dir
+// RUN: mkdir -p %t.dir
+// RUN: cp -r %S/* %t.dir/
+//
+// Check the build log.
+// RUN: %{swift-build} --package-path %t.dir 2>&1 | tee %t.build-log
+//
+// Verify that the build worked.
+// RUN: test -x %t.dir/.build/debug/exec
+//
+// RUN: %t.dir/.build/debug/exec > %t.out
+// RUN: %{FileCheck} --check-prefix CHECK-APP-OUTPUT --input-file %t.out %s
+// CHECK-APP-OUTPUT: 10
+// CHECK-APP-OUTPUT-NEXT: OK
+//
+// Try debugging the application.
+// RUN: %{lldb} %t.dir/.build/debug/exec -o "b core.swift:5" -o r -o "po value" -b &> %t.lldb
+// RUN: %{FileCheck} --check-prefix CHECK-LLDB-LOG --input-file %t.lldb %s
+// CHECK-LLDB-LOG: (lldb) po value
+// CHECK-LLDB-LOG-NEXT: 5
+

test-lldb-with-c-package/CFoo/foo.h

@@ -0,0 +1,7 @@
+import See
+
+public func core() -> Int {
+    var value = Int(see())
+    value = value * 2
+    return value
+}