ptrace.h: add new ptrace requests to get/set sigmask

PTRACE_GETSIGMASK and PTRACE_SETSIGMASK were added in linux v3.11
and used by checkpoint/restore tools

include/sys/ptrace.h

@@ -37,6 +37,8 @@ extern "C" {
 #define PTRACE_INTERRUPT 0x4207
 #define PTRACE_LISTEN 0x4208
 #define PTRACE_PEEKSIGINFO 0x4209
+#define PTRACE_GETSIGMASK 0x420a
+#define PTRACE_SETSIGMASK 0x420b
 
 #define PT_READ_I PTRACE_PEEKTEXT
 #define PT_READ_D PTRACE_PEEKDATA