atomic: check if -latomic is required for std::atomic

* configure.ac,
m4/l_atomic.m4,
python/Makefile.am,
tests/Makefile.am: Here.
9 jobs for er/spot3 in 92 minutes and 53 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #93452
alpine-gcc

00:55:37

passed #93453
arch-clang

00:44:38

passed #93454
arch-gcc-glibcxxdebug

01:17:14

passed #93451
debian-gcc-snapshot

01:20:23

passed #93449
debian-stable-gcc

01:20:30

passed #93450
debian-unstable-gcc-coverage

00:59:23

89.6%
passed #93455
mingw-shared

00:10:19

passed #93456
mingw-static

00:09:07

passed #93457
armv7
raspbian

01:32:50