OK, this is the big one. We still keep using `#include` guards only
where we absolutely need to, but with each header now being valid in
isolation, this can now actually help *minimize* the length of each
translation unit's `#include` list. Turns out that after removing all
the duplicates, we only *actually* need to guard 29 headers across all
5 games.
Part of P0285, funded by [Anonymous] and iruleatgames.
One of the rare cases where explicitly spelling out the FP_SEG() cast
is better than just calling the C++ wrapper: To drive home the point
that this code relies on `far` pointer semantics. Running the dialog
script performs arithmetic on only the offset part of this pointer, and
the segment part must remain unchanged for this hmem_free() call to
work as intended.
Completes P0186, funded by [Anonymous] and Blue Bolt.
nmlgc