x86_64: define reg names if not defined

_GNU_SOURCE can be defined without defining REG_X macros so it is not a
good indicator. (QEMU for example defines it in the build system.) x86
and x86_64 should have consistant looking defs.h so ifndef guards are
added to each REG_X definition.

arch/x86/defs.h

@@ -1,7 +1,6 @@
 #ifndef __ARCH_X86_DEFS_H
 #define __ARCH_X86_DEFS_H
 
-#ifndef _GNU_SOURCE
 #ifndef REG_GS
 # define REG_GS		(0)
 #endif
@@ -53,7 +52,6 @@
 #ifndef REG_EIP
 # define REG_EIP	(14)
 #endif
-#endif
 
 #define REG_SZ		(4)
 

arch/x86_64/defs.h

@@ -1,29 +1,95 @@
 #ifndef __ARCH_X86_64_DEFS_H
 #define __ARCH_X86_64_DEFS_H
 
-#ifndef _GNU_SOURCE
+#ifndef REG_R8
 # define REG_R8		(0)
+#endif
+
+#ifndef REG_R9
 # define REG_R9		(1)
+#endif
+
+#ifndef REG_R10
 # define REG_R10	(2)
+#endif
+
+#ifndef REG_R11
 # define REG_R11	(3)
+#endif
+
+#ifndef REG_R12
 # define REG_R12	(4)
+#endif
+
+#ifndef REG_R13
 # define REG_R13	(5)
+#endif
+
+#ifndef REG_R14
 # define REG_R14	(6)
+#endif
+
+#ifndef REG_R15
 # define REG_R15	(7)
+#endif
+
+#ifndef REG_RDI
 # define REG_RDI	(8)
+#endif
+
+#ifndef REG_RSI
 # define REG_RSI	(9)
+#endif
+
+#ifndef REG_RBP
 # define REG_RBP	(10)
+#endif
+
+#ifndef REG_RBX
 # define REG_RBX	(11)
+#endif
+
+#ifndef REG_RDX
 # define REG_RDX	(12)
+#endif
+
+#ifndef REG_RAX
 # define REG_RAX	(13)
+#endif
+
+#ifndef REG_RCX
 # define REG_RCX	(14)
+#endif
+
+#ifndef REG_RSP
 # define REG_RSP	(15)
+#endif
+
+#ifndef REG_RIP
 # define REG_RIP	(16)
+#endif
+
+#ifndef REG_EFL
 # define REG_EFL	(17)
+#endif
+
+#ifndef REG_CSGSFS
 # define REG_CSGSFS	(18)
+#endif
+
+#ifndef REG_ERR
 # define REG_ERR	(19)
+#endif
+
+#ifndef REG_TRAPNO
 # define REG_TRAPNO	(20)
+#endif
+
+#ifndef REG_OLDMASK
 # define REG_OLDMASK	(21)
+#endif
+
+#ifndef REG_CR2
 # define REG_CR2	(22)
 #endif