ELF: Properly redefine PT_GNU_* in terms of PT_LOOS

The PT_GNU_* program header types are actually offsets from PT_LOOS,
so redefine them as such, reorder them, and add the missing PT_GNU_RELRO.

Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

include/uapi/linux/elf.h

@@ -35,10 +35,11 @@ typedef __s64	Elf64_Sxword;
 #define PT_HIOS    0x6fffffff      /* OS-specific */
 #define PT_LOPROC  0x70000000
 #define PT_HIPROC  0x7fffffff
-#define PT_GNU_EH_FRAME		0x6474e550
-#define PT_GNU_PROPERTY		0x6474e553
-
+#define PT_GNU_EH_FRAME	(PT_LOOS + 0x474e550)
 #define PT_GNU_STACK	(PT_LOOS + 0x474e551)
+#define PT_GNU_RELRO	(PT_LOOS + 0x474e552)
+#define PT_GNU_PROPERTY	(PT_LOOS + 0x474e553)
+
 
 /*
  * Extended Numbering