We now have multiple instances of hand-rolled generators to manage export files for the cases where we need them:

• https://github.com/mongodb/mongo/blob/80c0edf953588717a1a7ed6b3734501ae6136a21/src/mongo/embedded/SConscript#L20-L38
• https://github.com/mongodb/mongo/blob/2752e6291178bb3df11f766985061bbba81f3b6d/src/third_party/IntelRDFPMathLib20U1/SConscript#L353-L393

They are actually all a little bit wrong: using the `csig` like that in the `for_signature` case is effective, in that it means if the file changes the target will be rebuilt, but it will be rebuilt because the signature of the action changed. That isn't really what happened though: the build action is really the same. Instead, if we wrote a scanner, then these would be picked up as implicit dependencies of the target automatically.

Build a tool to inject a scanner for export files and do all the magic automatically, then replace these usages. We should consider doing this for other places we are abusing the `csig` mechanism to detect changes, like in the sanitizer deny list setup.