SR-7309: Add tests for -static-executable on Linux

- Add extra test using Dispatch with -static-executable.

Author: spevans

test-static-executable/dispatch-static-executable.swift

@@ -0,0 +1,6 @@
+import Dispatch
+
+let queue = DispatchQueue(label: "queuename", attributes: .concurrent)
+queue.sync {
+    print("Dispatch")
+}

test-static-executable/dispatch-static-executable.test

@@ -0,0 +1,9 @@
+REQUIRES: platform=Linux
+RUN: rm -rf %t
+RUN: mkdir -p %t
+RUN: %{swiftc} -static-executable  -lDispatchStubs -lbsd -o %t/dispatch_test %S/dispatch-static-executable.swift
+RUN: %t/dispatch_test | %{FileCheck} %s
+RUN: file %t/dispatch_test | %{FileCheck} %s --check-prefix=FILE
+CHECK: Dispatch
+FILE: , statically linked,
+

test-static-executable/static-executable.swift

@@ -0,0 +1 @@
+print("OK")

test-static-executable/static-executable.test

@@ -0,0 +1,8 @@
+REQUIRES: platform=Linux
+RUN: rm -rf %t
+RUN: mkdir -p %t
+RUN: %{swiftc} -static-executable -o %t/static_executable %S/static-executable.swift
+RUN: %t/static_executable | %{FileCheck} %s
+RUN: file %t/static_executable | %{FileCheck} %s --check-prefix=FILE
+CHECK: OK
+FILE: , statically linked,