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/linker/linker_globals.h b/linker/linker_globals.h
index 11ccbd5..b470918 100644
--- a/linker/linker_globals.h
+++ b/linker/linker_globals.h
@@ -26,8 +26,7 @@
  * SUCH DAMAGE.
  */
 
-#ifndef __LINKER_GLOBALS_H
-#define __LINKER_GLOBALS_H
+#pragma once
 
 #include <link.h>
 #include <stddef.h>
@@ -86,5 +85,3 @@
  private:
   std::string saved_error_msg_;
 };
-
-#endif  /* __LINKER_GLOBALS_H */