Simple example of using two allocators in one application.

Example to simulate using two allocators in one application.  This will
be useful for scenarios in openenclave.

src/test/func/two_alloc_types/alloc1.cc

@@ -0,0 +1,10 @@
+#undef IS_ADDRESS_SPACE_CONSTRAINED
+#define OPEN_ENCLAVE
+#define OPEN_ENCLAVE_SIMULATION
+#define USE_RESERVE_MULTIPLE 1
+#define NO_BOOTSTRAP_ALLOCATOR
+#define IS_ADDRESS_SPACE_CONSTRAINED
+#define SNMALLOC_NAME_MANGLE(a) enclave_##a
+// Redefine the namespace, so we can have two versions.
+#define snmalloc snmalloc_enclave
+#include "../../../override/malloc.cc"

src/test/func/two_alloc_types/alloc2.cc

@@ -0,0 +1,6 @@
+#undef IS_ADDRESS_SPACE_CONSTRAINED
+#define SNMALLOC_NAME_MANGLE(a) host_##a
+#define NO_BOOTSTRAP_ALLOCATOR
+// Redefine the namespace, so we can have two versions.
+#define snmalloc snmalloc_host
+#include "../../../override/malloc.cc"

src/test/func/two_alloc_types/main.cc

@@ -0,0 +1,53 @@
+#include "../../../snmalloc.h"
+
+#include <iostream>
+#include <stdlib.h>
+#include <string.h>
+
+void* oe_base;
+void* oe_end;
+extern "C" const void* __oe_get_heap_base()
+{
+  return oe_base;
+}
+
+extern "C" const void* __oe_get_heap_end()
+{
+  return oe_end;
+}
+
+extern "C" void* oe_memset(void* p, int c, size_t size)
+{
+  return memset(p, c, size);
+}
+
+extern "C" void oe_abort()
+{
+  abort();
+}
+
+extern "C" void* host_malloc(size_t);
+extern "C" void host_free(void*);
+
+extern "C" void* enclave_malloc(size_t);
+extern "C" void enclave_free(void*);
+
+using namespace snmalloc;
+int main()
+{
+  DefaultPal pal;
+
+  size_t size = 1ULL << 28;
+  oe_base = pal.reserve<true>(&size, 0);
+  oe_end = (uint8_t*)oe_base + size;
+  std::cout << "Allocated region " << oe_base << " - " << oe_end << std::endl;
+
+  auto a = host_malloc(128);
+  auto b = enclave_malloc(128);
+
+  std::cout << "Host alloc " << a << std::endl;
+  std::cout << "Enclave alloc " << b << std::endl;
+
+  host_free(a);
+  enclave_free(b);
+}