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_relocs.h b/linker/linker_relocs.h
index ed00594..4bab0e0 100644
--- a/linker/linker_relocs.h
+++ b/linker/linker_relocs.h
@@ -26,8 +26,7 @@
  * SUCH DAMAGE.
  */
 
-#ifndef __LINKER_RELOCS_H
-#define __LINKER_RELOCS_H
+#pragma once
 
 #include <elf.h>
 
@@ -62,5 +61,3 @@
 #define R_GENERIC_IRELATIVE R_X86_64_IRELATIVE
 
 #endif
-
-#endif // __LINKER_RELOCS_H