Fix regression from #8108 (Mar 2023). Since that change, gocross has
always been rebuilt on each run of ./tool/go (gocross-wrapper.sh),
adding ~100ms. (Well, not totally rebuilt; cmd/go's caching still
ends up working fine.)
The problem was $gocross_path was just "gocross", which isn't in my
path (and "." isn't in my $PATH, as it shouldn't be), so this line was
always evaluating to the empty string:
gotver="$($gocross_path gocross-version 2>/dev/null || echo '')"
The ./gocross is fine because of the earlier `cd "$repo_root"`
Updates tailscale/corp#21262
Updates tailscale/corp#21263
Change-Id: I80d25446097a3bb3423490c164352f0b569add5f
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
b56058d7e3