Tracking "requested variants" and ways to "get rid of" outdated ones

[Mojca Miklavec]

Hi,

I like variants. But I believe that many of us are often bitten by the
inability to "get rid of" outdated variants without manual
intervention.

Typical examples:

- clang-3.x keeps changing its mind about whether +analyzer /
+arm_runtime should be the default or not. When the default is changed
and I want to upgrade, it starts compiling from source.

- Once I have "octave +gcc47" installed, it will be stuck with +gcc47
forever, even after the default has long been switched to +gcc48, then
+gcc49, ... Same is true for ld64 and the multiple clang variants.

I don't know how to properly handle that, but are there any chances to
at least track whether the user intentionally switched a variant
on/off/picked another variant? If we had that information the upgraded
port would have at least some chances to switch to the new default
variant (providing the user didn't explicitly mess with the variants
in that particular port). This would also be a lot more useful for
statistics (mpstat).

Mojca