I noticed that running the runes in docs/vendoring.md made a bunch of files
which are omitted by modern vndr come back, presumably due to the old version
of vndr referenced there. So update the go-compile package to the current
version everywhere.
Also correct the use of `make` variable syntax (`$(PWD)`) where shell syntax
command substitution for `pwd` was desired.
Signed-off-by: Ian Campbell <ijc@docker.com>