re PR go/66378 (libgo syscall.Sendfile() does not honor/use offset argument)

	PR go/66378
    syscall: Fix initial offset value in syscall.Sendfile.
    
    Bug reported in https://gcc.gnu.org/PR66378.
    
    Reviewed-on: https://go-review.googlesource.com/17159

From-SVN: r230699

gcc/go/gofrontend/MERGE

-81dcb1ba4de82a6c9325cb322d5a832a6b1f168d
+97ec885c715b3922b0866c081554899b8d50933a
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/syscall/libcall_bsd.go

@@ -17,6 +17,7 @@ func Sendfile(outfd int, infd int, offset *int64, count int) (written int, err e
 	var soff Offset_t
 	var psoff *Offset_t
 	if offset != nil {
+		soff = Offset_t(*offset)
 		psoff = &soff
 	}
 	written, err = sendfile(outfd, infd, psoff, count)

libgo/go/syscall/libcall_linux.go

@@ -327,6 +327,7 @@ func Sendfile(outfd int, infd int, offset *int64, count int) (written int, err e
 	var soff Offset_t
 	var psoff *Offset_t
 	if offset != nil {
+		soff = Offset_t(*offset)
 		psoff = &soff
 	}
 	written, err = sendfile(outfd, infd, psoff, count)