gmake and trace mode

[Ryan Schmidt]

If the gmake port is installed, then ports that use make will fail in trace mode, unless the port declares a dependency on the gmake port.

Some have taken to fixing this by adding a gmake dependency, e.g.:

https://github.com/macports/macports-ports/commit/7f46df47ef611c5a9c5a92ad3b552bb4acc35100

Is that the solution we want for all ports that use make? Or can we think of a different solution? Previously we were only adding a gmake dependency if the gmake installed by Xcode was unsuitable for some reason, and as far as I know that has been very rare, with the exception of on Tiger, whose gmake 3.80 is outdated.