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_gdb_support.h b/linker/linker_gdb_support.h
index 6709da1..4ae18ee 100644
--- a/linker/linker_gdb_support.h
+++ b/linker/linker_gdb_support.h
@@ -25,8 +25,8 @@
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
-#ifndef __LINKER_GDB_SUPPORT_H
-#define __LINKER_GDB_SUPPORT_H
+
+#pragma once
 
 #include <link.h>
 #include <sys/cdefs.h>
@@ -42,5 +42,3 @@
 extern struct r_debug _r_debug;
 
 __END_DECLS
-
-#endif