m68k: fix build

When <sys/reg.h> is included after <linux/ptrace.h>, the build fails
on m68k with the following diagnostics:

  In file included from /usr/include/linux/ptrace.h:101:0,
                   from ptrace.h:51,
                   from sigreturn.c:2:
  /usr/include/m68k-linux-gnu/sys/reg.h:26:3: error: expected identifier
  before numeric constant
     PT_D1 = 0,
     ^

Apparently, the only architecture where strace needs definitions
provided by <sys/reg.h> is x86_64, other three (m68k, tile, and x86)
are fine with definitions already provided by <linux/ptrace.h>.

Fix the issue by getting rid of <sys/reg.h> and defining necessary
macros in linux/x86_64/arch_regs.h file.

* configure.ac (AC_CHECK_HEADERS): Remove sys/reg.h.
* regs.h: Do not include <sys/reg.h>.
* linux/x86_64/arch_regs.h (R15, R14, R13, R12, RBP, RBX, R11, R10,
R9, R8, RAX, RCX, RDX, RSI, RDI, ORIG_RAX, RIP, CS, EFLAGS, RSP, SS,
FS_BASE, GS_BASE, DS, ES, FS, GS): New macros.
* NEWS: Mention this fix.

Fixes: v4.21~21 ("Include <sys/ptrace.h> early")

NEWS

@@ -1,6 +1,9 @@
 Noteworthy changes in release ?.?? (????-??-??)
 ===============================================
 
+* Bug fixes
+  * Fixed build on m68k.
+
 Noteworthy changes in release 4.21 (2018-02-13)
 ===============================================
 

configure.ac

@@ -436,7 +436,6 @@ AC_CHECK_HEADERS(m4_normalize([
 	sys/ipc.h
 	sys/msg.h
 	sys/quota.h
-	sys/reg.h
 	sys/sem.h
 	sys/shm.h
 	sys/signalfd.h

linux/x86_64/arch_regs.h

@@ -1,2 +1,31 @@
 extern uint32_t *const i386_esp_ptr;
 extern uint64_t *const x86_64_rsp_ptr;
+
+/* <asm/ptrace.h> does not provide these definitions.  */
+#define R15		0
+#define R14		1
+#define R13		2
+#define R12		3
+#define RBP		4
+#define RBX		5
+#define R11		6
+#define R10		7
+#define R9		8
+#define R8		9
+#define RAX		10
+#define RCX		11
+#define RDX		12
+#define RSI		13
+#define RDI		14
+#define ORIG_RAX	15
+#define RIP		16
+#define CS		17
+#define EFLAGS		18
+#define RSP		19
+#define SS		20
+#define FS_BASE		21
+#define GS_BASE		22
+#define DS		23
+#define ES		24
+#define FS		25
+#define GS		26

regs.h

@@ -2,11 +2,6 @@
 #define STRACE_REGS_H
 
 #include <sys/user.h>
-
-#ifdef HAVE_SYS_REG_H
-# include <sys/reg.h>
-#endif
-
 #include "arch_regs.h"
 
 #endif /* !STRACE_REGS_H */