Add execution test for #dsohandle: multiple images

There wasn't an execution test involving #dsohandle, so add one here.
Also, the DSO handle coming from different modules should never be
the same.

rdar://problem/26565092

Author: bitjammer

validation-test/execution/Inputs/dsohandle-first.swift

@@ -0,0 +1,3 @@
+public func getFirstDSOHandle() -> UnsafeRawPointer {
+  return #dsohandle
+}

validation-test/execution/Inputs/dsohandle-second.swift

@@ -0,0 +1,3 @@
+public func getSecondDSOHandle() -> UnsafeRawPointer {
+  return #dsohandle
+}

validation-test/execution/dsohandle-multi-module.swift

@@ -0,0 +1,22 @@
+// RUN: rm -rf %t && mkdir %t
+
+// RUN: (cd %t && %target-build-swift %S/Inputs/dsohandle-first.swift -emit-library -emit-module -module-name first)
+// RUN: (cd %t && %target-build-swift %S/Inputs/dsohandle-second.swift -emit-library -emit-module -module-name second)
+// RUN: %target-build-swift -I %t -L %t -lfirst -lsecond %s -o %t/main
+// RUN: env LD_LIBRARY_PATH=%t DYLD_LIBRARY_PATH=%t %target-run %t/main
+// REQUIRES: executable_test
+
+import first
+import second
+
+import StdlibUnittest
+
+let DSOHandleTests = TestSuite("DSOHandle")
+
+DSOHandleTests.test("Unique handles for different images") {
+  let firstHandle = getFirstDSOHandle()
+  let secondHandle = getSecondDSOHandle()
+  expectNotEqual(firstHandle, secondHandle)
+}
+
+runAllTests()