Technically not bloat if we imagine a development setting where ZUN
ran ZUN_RES.COM once and then repeatedly deleted HUUHI.DAT while
leaving ZUN_RES.COM resident.
Part of P0285, funded by [Anonymous] and iruleatgames.
I considered disabling it by default and only enabling it through an
optional `CONFIG_RESEARCH` variable, but that turned out to be too
annoying and inconsistent when `build_dumb.bat` generation came into
play.
Part of P0004, funded by GhostPhanom.
`tup generate` does this as well, but only emits the `mkdir` calls for
the directories that are missing in the current working tree, requiring
a clean checkout to actually emit all necessary ones. This is much more
convenient.
Part of P0282, funded by [Anonymous].