Because of the nature of the interpreter, these headers should be
loaded/unloaded on an as-needed basis.
This commit is particularly useful for pluggables in that, if the
pluggable requires that the `dfi` API (or API-related implementations)
have certain preprocessor requisites fulfilled for the pluggable, the
API can now be compiled *after* the pluggable has been loaded but also
*before* the pluggable *requires* the use of the API (or API-related).
In other words, without this commit, a pluggable's `#define`s will be
useless *after* the API (or API-related implementations) is loaded and
compiled (at least not without an API reload, but that is not needed).
NOTE: this change does not affect `dfi`'s pluggable auto-(un|re)loading,
as the pluggable will have already been loaded prior to any other `dfi`
API compiling.
Aaron Fiore
6f415bd847
