Add helper functions and files for gpt tests.

src/platform/vboot_reference/common/utility_stub.c

Index: src/platform/vboot_reference/common/utility_stub.c
diff --git a/src/platform/vboot_reference/common/utility_stub.c b/src/platform/vboot_reference/common/utility_stub.c
index d2244c797b2d43549a9531e57e367feb77c05890..66132703ea63e57d13d2d9c364a89ed1e5679081 100644
--- a/src/platform/vboot_reference/common/utility_stub.c
+++ b/src/platform/vboot_reference/common/utility_stub.c
@@ -42,6 +42,10 @@ void Free(void* ptr) {
   free(ptr);
 }
 
+int Memcmp(const void* src1, const void* src2, size_t n) {
+  return memcmp(src1, src2, n);
+}
+
 void* Memcpy(void* dest, const void* src, size_t n) {
   return memcpy(dest, src, n);
 }