Set SYSCALL_NEVER_FAILS flag for getpid, getppid and gettid syscall

* linux/*/syscallent*.h (getpid, getppid, gettid): Set NF flag.
diff --git a/linux/s390x/syscallent.h b/linux/s390x/syscallent.h
index 22e1e86..9f11018 100644
--- a/linux/s390x/syscallent.h
+++ b/linux/s390x/syscallent.h
@@ -47,7 +47,7 @@
 [ 17] = { },
 [ 18] = { },
 [ 19] = { 3,	TD,		SEN(lseek),			"lseek"			},
-[ 20] = { 0,	0,		SEN(getpid),			"getpid"		},
+[ 20] = { 0,	NF,		SEN(getpid),			"getpid"		},
 [ 21] = { 5,	TF,		SEN(mount),			"mount"			},
 [ 22] = { 1,	TF,		SEN(umount),			"umount"		},
 [ 23] = { },
@@ -91,7 +91,7 @@
 [ 61] = { 1,	TF,		SEN(chroot),			"chroot"		},
 [ 62] = { 2,	0,		SEN(ustat),			"ustat"			},
 [ 63] = { 2,	TD,		SEN(dup2),			"dup2"			},
-[ 64] = { 0,	0,		SEN(getppid),			"getppid"		},
+[ 64] = { 0,	NF,		SEN(getppid),			"getppid"		},
 [ 65] = { 0,	0,		SEN(getpgrp),			"getpgrp"		},
 [ 66] = { 0,	0,		SEN(setsid),			"setsid"		},
 [ 67] = { 3,	TS,		SEN(sigaction),			"sigaction"		},
@@ -248,7 +248,7 @@
 [233] = { 2,	TF,		SEN(removexattr),		"removexattr"		},
 [234] = { 2,	TF,		SEN(removexattr),		"lremovexattr"		},
 [235] = { 2,	TD,		SEN(fremovexattr),		"fremovexattr"		},
-[236] = { 0,	0,		SEN(gettid),			"gettid"		},
+[236] = { 0,	NF,		SEN(gettid),			"gettid"		},
 [237] = { 2,	TS,		SEN(kill),			"tkill"			},
 [238] = { 6,	0,		SEN(futex),			"futex"			},
 [239] = { 3,	0,		SEN(sched_setaffinity),		"sched_setaffinity"	},