Switch the rest of our internal headers to #pragma once.

We've been using #pragma once for new internal files, but let's be more bold.

Bug: N/A
Test: builds
Change-Id: I7e2ee2730043bd884f9571cdbd8b524043030c07
diff --git a/libc/malloc_debug/OptionData.h b/libc/malloc_debug/OptionData.h
index 5c2d272..3fa8e14 100644
--- a/libc/malloc_debug/OptionData.h
+++ b/libc/malloc_debug/OptionData.h
@@ -26,8 +26,7 @@
  * SUCH DAMAGE.
  */
 
-#ifndef DEBUG_MALLOC_OPTIONDATA_H
-#define DEBUG_MALLOC_OPTIONDATA_H
+#pragma once
 
 // Forward Declarations
 class DebugData;
@@ -42,5 +41,3 @@
 
   DISALLOW_COPY_AND_ASSIGN(OptionData);
 };
-
-#endif // MALLOC_DEBUG_OPTIONDATA_H