samples: add Terra samples

source: https://github.com/zdevito/terra/tree/master/tests

samples/Terra/cunion2.t

@@ -0,0 +1,35 @@
+local C = terralib.includecstring [[
+
+union testunion {
+  int idata;
+  float fdata;
+};
+
+void setUnionI(union testunion * u){
+  u->idata = 3;
+}
+void setUnionF(union testunion * u){
+  u->fdata = 4.f;
+}
+
+]]
+
+terra foo() : int
+  var u : C.testunion
+  C.setUnionI(&u)
+  var f = u.idata
+  C.setUnionF(&u)
+  var f2 = u.fdata
+  return f + f2
+end
+
+terra foo2()
+  var a : C.testunion
+  a.fdata = -3.0
+  a.idata = a.idata and not (1 << 31)
+  return a.fdata
+end
+
+local test = require("test")
+test.eq(foo(),7)
+test.eq(foo2(),3)