[release-branch.go1.12] path/filepath: don't discard .. in EvalSymlinks
EvalSymlinks was mishandling cases like "/x/../../y" or "../../../x"
where there is an extra ".." that goes past the start of the path.
Updates #30520
Fixes #30586
Change-Id: I07525575f83009032fa1a99aa270c8d42007d276
Reviewed-on: https://go-review.googlesource.com/c/go/+/164762
Reviewed-by: Bryan C. Mills <bcmills@google.com>
(cherry picked from commit
294edb272d5d145665bdf8b4254609eae0363a8d)
Reviewed-on: https://go-review.googlesource.com/c/go/+/165197
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>