Upstream libuv commits:
left an asymmetry in the way O_NONBLOCK is set and cleared. Normally ioctl/FIONBIO is used for both. However, uv_spawn uses fcntl/O_NONBLOCK to clear O_NONBLOCK between fork and exec. This fails on Linux/sparc64 where setting via ioctl/FIONBIO actually sets two bits (in O_NDELAY) that cause clearing via fcntl/O_NONBLOCK to be silently ignored (though clearing via ioctl/FIONBIO or fcntl/O_NDELAY works).
Since CMake MR !1455 (merged), CTest uses libuv. On Linux/sparc64
child processes have been started with non-blocking output pipes. This
can lead to write errors or lost output from children not prepared to
EAGAIN on stdout or stderr.
Fix this for now by switching libuv back to fcntl/O_NONBLOCK to set and clear O_NONBLOCK when compiled on Linux/sparc64.
Fixes: #17941 (closed)