bug#47454: plist-put should have a version which accepts multiple properties

[Juri Linkov]

> (setf (seq-elt plist ...))
>
> may help with that, though.

BTW, often after pulling from master and recompiling,
Emacs fails to start with such errors:

Debugger entered--Lisp error: (error "(setf seq-elt) is already defined as 
something else than a generic function")
  error("%s is already defined as something else than a generic function" 
\(setf\ seq-elt\))
  cl-generic-ensure-function(\(setf\ seq-elt\))
  cl-generic-define-method(\(setf\ seq-elt\) nil (store (sequence array) n) nil 
#f(compiled-function (store sequence n) #<bytecode -0x1d67862086490644>))
  byte-code(...)
  require(seq)
  byte-cod...)
  require(gnus-util)
  byte-code(...)
  require(nnheader)
  byte-code(...)
  require(gnus)

This requires bootstrap that fixes it.
But I wonder if maybe there is some deeply hidden problem with setf and seq-elt?