unix: define Time_t for FreeBSD

Fixes golang/go#48148

Change-Id: I8c0a62b204689fc6ac9e29b1ba0b084e3d807323
Reviewed-on: https://go-review.googlesource.com/c/sys/+/348012
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
diff --git a/unix/ztypes_freebsd_arm.go b/unix/ztypes_freebsd_arm.go
index dce0a5c..19223ce 100644
--- a/unix/ztypes_freebsd_arm.go
+++ b/unix/ztypes_freebsd_arm.go
@@ -33,6 +33,8 @@
 	_    [4]byte
 }
 
+type Time_t int32
+
 type Rusage struct {
 	Utime    Timeval
 	Stime    Timeval