syscall-emul: Add the tgkill system call

This changeset adds support to kill a thread group by calling
the tgkill system call. The functionality is needed in some
pthread applications.

Change-Id: I0413a3331be69b74dfab30de95384113ec4efb63
Reviewed-on: https://gem5-review.googlesource.com/2268
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Michael LeBeane <Michael.Lebeane@amd.com>

src/arch/x86/linux/process.cc

@@ -454,7 +454,7 @@ static SyscallDesc syscallDescs64[] = {
     /* 231 */ SyscallDesc("exit_group", exitGroupFunc),
     /* 232 */ SyscallDesc("epoll_wait", unimplementedFunc),
     /* 233 */ SyscallDesc("epoll_ctl", unimplementedFunc),
-    /* 234 */ SyscallDesc("tgkill", unimplementedFunc),
+    /* 234 */ SyscallDesc("tgkill", tgkillFunc<X86Linux64>),
     /* 235 */ SyscallDesc("utimes", unimplementedFunc),
     /* 236 */ SyscallDesc("vserver", unimplementedFunc),
     /* 237 */ SyscallDesc("mbind", unimplementedFunc),
@@ -819,7 +819,7 @@ static SyscallDesc syscallDescs32[] = {
     /* 267 */ SyscallDesc("clock_nanosleep", unimplementedFunc),
     /* 268 */ SyscallDesc("statfs64", unimplementedFunc),
     /* 269 */ SyscallDesc("fstatfs64", unimplementedFunc),
-    /* 270 */ SyscallDesc("tgkill", unimplementedFunc),
+    /* 270 */ SyscallDesc("tgkill", tgkillFunc<X86Linux32>),
     /* 271 */ SyscallDesc("utimes", unimplementedFunc),
     /* 272 */ SyscallDesc("fadvise64_64", unimplementedFunc),
     /* 273 */ SyscallDesc("vserver", unimplementedFunc),