[S390] add breaking event address for user space

Copy the last breaking event address from the lowcore to a new
field in the thread_struct on each system entry. Add a new
ptrace request PTRACE_GET_LAST_BREAK and a new utrace regset
REGSET_LAST_BREAK to query the last breaking event.

This is useful for debugging wild branches in user space code.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/include/linux/elf.h b/include/linux/elf.h
index 5978584..4d60801 100644
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -394,6 +394,7 @@
 #define NT_S390_TODPREG	0x303		/* s390 TOD programmable register */
 #define NT_S390_CTRS	0x304		/* s390 control registers */
 #define NT_S390_PREFIX	0x305		/* s390 prefix register */
+#define NT_S390_LAST_BREAK	0x306	/* s390 breaking event address */
 
 
 /* Note header in a PT_NOTE section */