new module 'simple-atomic'

[Bruno Haible]

Most lock-free algorithms use the compare-and-swap primitive in one form or
another. In order to be able to implement such algorithms, here is a module
that implements compare-and-swap for 32-bit words and pointer-sized words.
It's far from a complete <stdatomic.h>, just the bare essentials.

Support for compilers that are not GCC compatible does require work, namely
finding the instructions generated by GCC and putting them in a form that
the non-GCC compiler can grok. So far, this has only been needed for AIX
and Solaris, and fortunately both support inline asms (so that no external .s
file is needed).


2021-02-14  Bruno Haible  <bruno@clisp.org>

        simple-atomic: Add tests.
        * tests/test-simple-atomic.c: New file.
        * modules/simple-atomic-tests: New file.

        simple-atomic: New module.
        * lib/simple-atomic.h: New file.
        * lib/simple-atomic.c: New file, based on lib/asyncsafe-spin.c.
        * modules/simple-atomic: New file.

0001-simple-atomic-New-module.patch
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0002-simple-atomic-Add-tests.patch
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