For IPC, squid creates a socket file in /var/run/squid, but this
directory does not exist. Because /run (/var/run) lives in tmpfs, you
cannot rely on it being created by the package.

Use `checkpath` in the initd file to make sure this path exists.

Fixes #11249

ref #10946

fixes #10665

Also expand the -latomic fix to cover the out-of-tree mipseln8hf.

While squid uses the proper autoconf logic to check if the -latomic is required
for 64-bit atomics, its conftest.cpp fails to compile without -fpermissive thus
yielding wrong result on 32-bit MIPS (which, until R6, lacks 64-bit atomics).

Do not bother with configure{.ac} patches (too bulky), do not add -fpermissive
to CXXFLAGS just to fix the conftest.cpp compilation (may affect too much) but
simply pass -latomic preemptibly on mips{el}.

As usual (no previous mips* apks exist, other architectures are unaffected),
keep pkgrel intact.

This commit should be removed when (if) upstream (or, really, autoconf) fixes
the problem.