add C++ placement new unit test

tests/Unit/HC/placement_new.cpp

@@ -0,0 +1,52 @@
+// XFAIL: Linux
+// RUN: %hc %s -lhc_am -o %t.out && %t.out
+
+#include <cstdlib>
+#include <cstdio>
+#include <hc.hpp>
+#include <hc_am.hpp>
+
+class Point {
+public:
+  int x;
+  int y;
+  int z;
+
+  /* hcc requires an explicit dtor?? */
+  ~Point() [[hc,cpu]] {}
+};
+
+int main() {
+
+  hc::extent<1> grid(64);
+  hc::accelerator acc;
+  char* gpu_buffer = hc::am_alloc(sizeof(Point)*grid[0], acc, 0);
+
+  hc::parallel_for_each(grid,[=](hc::index<1> idx) [[hc]] {
+     auto p = new(gpu_buffer + sizeof(Point) * idx[0]) Point;
+     p->x = idx[0];
+     p->y = 0;
+     p->z = 0;
+     p->~Point();
+  }).wait();
+
+  char* buffer = (char*)malloc(sizeof(Point)*grid[0]);
+  hc::am_copy(buffer, gpu_buffer, sizeof(Point)*grid[0]);
+  hc::am_free(gpu_buffer);
+
+  int errors = 0;
+  for (int i = 0; i < grid[0]; i++) {
+    auto p = new(buffer+sizeof(Point)*i) Point;
+    if (p->x != i
+       || p->y != 0
+       || p->z != 0) {
+      errors++;
+    }
+#ifdef DEBUG
+    printf("Point[%d]: x=%d, y=%d, z=%d\n",i,p->x,p->y,p->z);
+#endif
+    p->~Point();
+  }
+  free(buffer);
+  return errors;
+}