irt: tools/squashfs4: enable parallel builds

[Elliott Mitchell]

Am I the only person who finds commit 3efd49a588
("tools/squashfs4: enable parallel builds") a bit odd?  Specifically from
the commit message:

> Run `time make tools/squashfs4/{clean,compile} -j$(nproc)`
> Before:
> real    0m8.803s
> user    0m12.415s
> sys     0m1.317s
> After:
> real    0m13.781s
> user    0m13.290s
> sys     0m1.528s

So a parallel build of squashfs4 took more processor time in user mode,
more processor time in supervisor mode, and *more* wall clock time?

More processor time is fine, that comes with coordinating parallel build
processes.  The goal of parallel builds is to spend a bit of processor
time to *reduce* wall clock time use.  Yet a parallel build of
`squashfs4` is stated to have resulted in a 50% increase?

Uhm.  Perhaps your computer's processor interconnect is very slow?
Does this computer have an extremely high processor count?  I do note
`squashfs4` doesn't have very many source files.

Generally I would support the use of parallel builds, but unless I'm
missing something this appears the case where it should be avoided.


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