Re: [toplevel] Fix make install (PR 22440)

[Paolo Bonzini <paolo dot bonzini at lu dot unisi dot ch>]

> Not quite.  Although they do act as subroutines, there's nothing to
> stop them from being processed in parallel, unless you explicitly add
> deps to serialize them.
For toplevel bootstrap, there is a .NOTPARALLEL in the makefile.  
Removing it is near the top of my todo list, just after *enabling* 
toplevel bootstrap...

I think Serge's patch should go in as it mimicks exactly what is done 
for "all" and other targets.  I promise to fix it asap.

Paolo