[hadrian] Rebuild programs on dynamicGhcPrograms/ghcProfiled change

Currently, if you change these ^ flavour parameters, rebuilding is not
triggered, since `programContext` doesn't set up a dependency on
those values.

Exposing these values via an oracle does set the dependency and
properly triggers a rebuild of binaries.

Several attempts to factor out these actions ended up in cyclic
dependency here or there. I'm not absolutely happy with this variant
either, but at least it works.

====

Issue repro:

In UserSettings.hs:
```
dbgDynamic = defaultFlavour { name = "dbg-dynamic"
                            , dynamicGhcPrograms = pure True,
                            ... }

dbgStatic = defaultFlavour { name = "dbg-static"
                           , dynamicGhcPrograms = pure False
                           ... }
```

Then in console:

```
$ hadrian/build.sh -j --flavour=dbg-dynamic
... does the build
$ hadrian/build.sh -j --flavour=dbg-static
... does nothing, considers binaries up to date
```

1 files changed, 1 insertions, 0 deletions

diff --git a/hadrian/src/Rules/Program.hs b/hadrian/src/Rules/Program.hs
index b5dde25624..6273f3da4d 100644
--- a/hadrian/src/Rules/Program.hs
+++ b/hadrian/src/Rules/Program.hs
@@ -12,6 +12,7 @@ import Oracles.Setting (topDirectory)
 import Packages
 import Settings
 import Settings.Default
+import Settings.Program (programContext)
 import Target
 import Utilities
 import Rules.Library