bug#64819: 30.0.50; condition-wait not interruptible

[Helmut Eller]

When Emacs is blocked in condition-wait, then C-g doesn't seem to work.
E.g. Emacs hangs and pressing C-g has no apparent effect when executing
the attached file with:

  emacs -Q -l deadlock.el -f deadlock

Mabye sys_cond_wait could call pthread_cond_timedwait with a fairly long
timeout, say one second, and repeatedly check if C-g was pressed.

deadlock.el
Description: application/emacs-lisp

Configured using:
 'configure --with-xpm=ifavailable --with-jpeg=ifavailable
 --with-gif=ifavailable --with-tiff=ifavailable'

Configured features:
CAIRO DBUS FREETYPE GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG LIBSELINUX
LIBSYSTEMD LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG SECCOMP SOUND
SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS WEBP X11 XDBE XIM XINPUT2 GTK3
ZLIB

Important settings:
  value of $LANG: C.UTF-8
  locale-coding-system: utf-8-unix