add spec for building a shared library using D

build_tests/shared_library/shared_library_d.rb

@@ -0,0 +1,9 @@
+Rscons::Environment.new do |env|
+  env["CPPPATH"] << "src/lib"
+  libmine = env.SharedLibrary("libmine", Dir["src/lib/*.d"])
+  env.Program("test-shared.exe",
+              Dir["src/*.c"],
+              "LIBPATH" => %w[.],
+              "LIBS" => %w[mine])
+  env.build_after("test-shared.exe", libmine.to_s)
+end

build_tests/shared_library/src/lib/one.d

@@ -0,0 +1,6 @@
+import core.stdc.stdio;
+
+extern (C) void one()
+{
+    printf("Hi from one()\n");
+}

build_tests/shared_library/src/lib/two.d

@@ -0,0 +1,6 @@
+import core.stdc.stdio;
+
+extern (C) void two()
+{
+    printf("Hi from two()\n");
+}