deps: make V8 compatible with older glibc

Remove call to `memfd_create`.
The function that references it is only used for V8 testing.

Refs: nodejs/node-v8#220

common.gypi

@@ -36,7 +36,7 @@
 
     # Reset this number to 0 on major V8 upgrades.
     # Increment by one for each non-official patch applied to deps/v8.
-    'v8_embedder_string': '-node.6',
+    'v8_embedder_string': '-node.7',
 
     ##### V8 defaults for Node.js #####
 

deps/v8/src/base/platform/platform-posix.cc

@@ -576,15 +576,7 @@ void OS::FreeAddressSpaceReservation(AddressSpaceReservation reservation) {
 #if !defined(V8_OS_MACOS)
 // static
 PlatformSharedMemoryHandle OS::CreateSharedMemoryHandleForTesting(size_t size) {
-#if V8_OS_LINUX && !V8_OS_ANDROID
-  const char* name = "V8MemFDForTesting";
-  int fd = memfd_create(name, MFD_CLOEXEC);
-  if (fd == -1) return kInvalidSharedMemoryHandle;
-  CHECK_EQ(0, ftruncate(fd, size));
-  return SharedMemoryHandleFromFileDescriptor(fd);
-#else
   return kInvalidSharedMemoryHandle;
-#endif
 }
 
 // static