See 6f1c0f7cc7 for part 1.
Turns out startup.elc likely exists on most Emacs installations (and,
since it's so integral to Emacs, it likely gets special treatment), so
it was a poor heuristic for this fix. Instead, a more variable target
would be calc-loaddefs.el.
On some systems, only calc-loaddefs.el.gz exists (in which case, we
should turn off the optimization). On others, calc-loaddefs.el
exists (so I'll assume it's safe to leave them on). I won't check for
calc-loaddefs.elc because it doesn't matter; calc.el explicitly
calls (load "calc-loaddefs.el") so it is never loaded.
Of course, you can sidestep the entire issue by building Emacs with
--without-compress-install, but it's not practical for users to
know/want to do that.
Amend: 6f1c0f7cc7
1d8c61698b