[Bug target/109166] Built-in __atomic_test_and_set does not seem to be atomic on ARMv4T

[hp at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109166

--- Comment #7 from Hans-Peter Nilsson <hp at gcc dot gnu.org> ---
(In reply to Hans-Peter Nilsson from comment #6)
> The cause  I guess, is just a bad fall-through in the arm/sync.md.

Or rather, optabs.cc:expand_atomic_test_and_set, which makes this issue
somewhat less target-specific.  To wit:
/* Failing all else, assume a single threaded environment and simply
   perform the operation.  */