Add integration tests for static-linking of Foundation (#87)

Implementation: apple/swift-corelibs-foundation#2996 and apple/swift#35936

test-foundation-package/test-foundation-networking-static-stdlib.test

@@ -0,0 +1,11 @@
+REQUIRES: platform=Linux
+RUN: rm -rf %t
+RUN: mkdir -p %t
+RUN: %{swiftc} -static-stdlib %S/test-foundation-networking.swift -o %t/test-foundation-networking
+RUN: %t/test-foundation-networking | %{FileCheck} %s
+RUN: ldd %t/test-foundation-networking | %{FileCheck} --check-prefix LDD %s
+
+CHECK: http://example.com
+LDD-NOT: libFoundation.so
+LDD-NOT: libFoundationNetworking.so
+LDD-NOT: libCoreFoundation.so

test-foundation-package/test-foundation-networking.swift

@@ -4,3 +4,8 @@ import FoundationNetworking
 let url = URL(string: "http://example.com")!
 let urlRequest = URLRequest(url: url)
 print(urlRequest)
+
+let urlSession = URLSession.shared
+let task = urlSession.dataTask(with: urlRequest)
+print(task.state)
+task.cancel()

test-foundation-package/test-foundation-static-stdlib.test

@@ -0,0 +1,12 @@
+REQUIRES: platform=Linux
+RUN: rm -rf %t
+RUN: mkdir -p %t
+RUN: %{swiftc} -static-stdlib %S/main.swift -o %t/main
+RUN: %t/main | %{FileCheck} %s
+RUN: ldd %t/main | %{FileCheck} --check-prefix LDD %s
+
+CHECK: Printing URL
+CHECK-NEXT: /tmp
+CHECK-NEXT: Done printing URL
+LDD-NOT: libFoundation.so
+LDD-NOT: libCoreFoundation.so

test-foundation-package/test-foundation-xml-static-stdlib.test

@@ -0,0 +1,10 @@
+REQUIRES: platform=Linux
+RUN: rm -rf %t
+RUN: mkdir -p %t
+RUN: %{swiftc} -static-stdlib %S/test-foundation-xml.swift -o %t/test-foundation-xml
+RUN: %t/test-foundation-xml | %{FileCheck} %s
+RUN: ldd %t/test-foundation-xml | %{FileCheck} --check-prefix LDD %s
+CHECK: NSXMLDocument
+LDD-NOT: libFoundation.so
+LDD-NOT: libFoundationXML.so
+LDD-NOT: libCoreFoundation.so