[build] Mark GDB stub as forbidden for UEFI Secure Boot

Enabling the GDB debugger functionality would provide an immediate and
trivial Secure Boot exploit.  Mark all GDB-related files as explicitly
forbidden for UEFI Secure Boot.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/core/gdbidt.S

@@ -1,3 +1,5 @@
+FILE_SECBOOT ( FORBIDDEN );
+
 /*
  * Interrupt handlers for GDB stub
  */

src/arch/i386/include/bits/gdbmach.h

@@ -10,6 +10,8 @@
  *
  */
 
+FILE_SECBOOT ( FORBIDDEN );
+
 #include <stdint.h>
 
 typedef unsigned long gdbreg_t;

src/arch/x86/core/gdbmach.c

@@ -23,6 +23,7 @@
  */
 
 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+FILE_SECBOOT ( FORBIDDEN );
 
 #include <stddef.h>
 #include <stdio.h>

src/arch/x86_64/core/gdbidt.S

@@ -22,6 +22,7 @@
  */
 
 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+FILE_SECBOOT ( FORBIDDEN );
 
 /** @file
  *

src/arch/x86_64/include/bits/gdbmach.h

@@ -10,6 +10,8 @@
  *
  */
 
+FILE_SECBOOT ( FORBIDDEN );
+
 #include <stdint.h>
 
 typedef unsigned long gdbreg_t;