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>

unix/types_freebsd.go

@@ -141,6 +141,8 @@ type Timespec C.struct_timespec
 
 type Timeval C.struct_timeval
 
+type Time_t C.time_t
+
 // Processes
 
 type Rusage C.struct_rusage

unix/ztypes_freebsd_386.go

@@ -31,6 +31,8 @@ type Timeval struct {
 	Usec int32
 }
 
+type Time_t int32
+
 type Rusage struct {
 	Utime    Timeval
 	Stime    Timeval

unix/ztypes_freebsd_amd64.go

@@ -31,6 +31,8 @@ type Timeval struct {
 	Usec int64
 }
 
+type Time_t int64
+
 type Rusage struct {
 	Utime    Timeval
 	Stime    Timeval

unix/ztypes_freebsd_arm.go

@@ -33,6 +33,8 @@ type Timeval struct {
 	_    [4]byte
 }
 
+type Time_t int32
+
 type Rusage struct {
 	Utime    Timeval
 	Stime    Timeval

unix/ztypes_freebsd_arm64.go

@@ -31,6 +31,8 @@ type Timeval struct {
 	Usec int64
 }
 
+type Time_t int64
+
 type Rusage struct {
 	Utime    Timeval
 	Stime    Timeval