add spec for building a shared library using D

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");
+}