libgo: update Makefile.in, accidentally omitted from last change
libgo: update Makefile.in, accidentally omitted from last change

Issue golang/go#19200

Change-Id: I1ebf1a16db692546f72ec76079bc57cd3dcd4d65
Reviewed-on: https://go-review.googlesource.com/38310
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/gofrontend,golang/gofrontend,golang/gofrontend,golang/gofrontend