Remove several race conditions with signal handler (bug #61370). This patch removes several race conditions between the interpreter and the Ctrl-C signal handler, as described in more detail in bug #61370. * libinterp/corefcn/sighandlers.h: Make can_interrupt atomic. * libinterp/corefcn/sighandlers.cc: Make can_interrupt, signals_caught atomic, use atomic value read for signals_caught, octave_interrupt_state, change 1 to true. * liboctave/util/quit.h: Move octave_interrupt_state and octave_signal_caught to C++ only code, rewrite octave_quit() function, rewrite OCTAVE_QUIT macro to use octave_quit_c() function. * liboctave/util/quit.cc: Make octave_interrupt_state and octave_signal_caught atomic, add new wrapper function octave_quit_c(). * libinterp/corefcn/interpreter.h: Make octave_initialized atomic. * libinterp/corefcn/interpreter.cc: Make octave_initialized atomic, change 0 to false. * liboctave/util/action-container.h: New namespace "util", make m_val atomic. * liboctave/util/oct-atomic.c: Reorder preprocessor if-elif-else ladder. * liboctave/util/cmd-edit.cc: Change 0 to false.

--- a/liboctave/util/oct-atomic.c	Sat Dec 03 13:55:14 2022 +0100
+++ b/liboctave/util/oct-atomic.c	Sat Dec 03 10:36:59 2022 -0500
@@ -29,9 +29,23 @@
 
 #include "oct-atomic.h"
 
+#if defined (__GNUC__)
+
+octave_idx_type
+octave_atomic_increment (octave_idx_type *x)
+{
+  return __sync_add_and_fetch (x,  1);
+}
+
+octave_idx_type
+octave_atomic_decrement (octave_idx_type *x)
+{
+  return __sync_sub_and_fetch (x, 1);
+}
+
 /* Some versions of GCC can't compile stdatomic.h with -fopenmp.  */
 
-#if defined (OCTAVE_STDATOMIC_H_OK)
+#elif defined (OCTAVE_STDATOMIC_H_OK)
 #  include <stdatomic.h>
 
 octave_idx_type
@@ -52,20 +66,6 @@
   return *x;
 }
 
-#elif defined (__GNUC__)
-
-octave_idx_type
-octave_atomic_increment (octave_idx_type *x)
-{
-  return __sync_add_and_fetch (x,  1);
-}
-
-octave_idx_type
-octave_atomic_decrement (octave_idx_type *x)
-{
-  return __sync_sub_and_fetch (x, 1);
-}
-
 #elif defined (_MSC_VER)
 #  include <intrin.h>