Make header include guards great again

i.e. #ifndef VM_WHATEVER -> #ifndef RUNTIME_VM_WHATEVER

This lets us remove a hack from the PRESUBMIT.py script that existed
for reasons that are no longer valid, and sets us up to add some
presubmit checks for the GN build.

R=asiva@google.com, rmacnak@google.com

Review URL: https://codereview.chromium.org/2450713004 .
diff --git a/runtime/vm/proccpuinfo.h b/runtime/vm/proccpuinfo.h
index 0814c6a..e81d7ee 100644
--- a/runtime/vm/proccpuinfo.h
+++ b/runtime/vm/proccpuinfo.h
@@ -2,8 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-#ifndef VM_PROCCPUINFO_H_
-#define VM_PROCCPUINFO_H_
+#ifndef RUNTIME_VM_PROCCPUINFO_H_
+#define RUNTIME_VM_PROCCPUINFO_H_
 
 #include "vm/globals.h"
 #if defined(TARGET_OS_LINUX) || defined(TARGET_OS_ANDROID)
@@ -31,4 +31,4 @@
 
 #endif  // defined(TARGET_OS_LINUX) || defined(TARGET_OS_ANDROID)
 
-#endif  // VM_PROCCPUINFO_H_
+#endif  // RUNTIME_VM_PROCCPUINFO_H_