Clarify of sig_atomic_t usage (got from Mutt).

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>

configure.ac

@@ -186,6 +186,40 @@ AC_TYPE_UID_T
 AC_STRUCT_ST_BLOCKS
 AC_CHECK_MEMBERS([struct stat.st_blksize, struct stat.st_rdev])
 
+AH_TEMPLATE([sig_atomic_t],
+            [/* Define to `int' if <signal.h> doesn't define.])
+AH_TEMPLATE([SIG_ATOMIC_VOLATILE_T],
+            [Some systems declare sig_atomic_t as volatile, some others -- no.
+             This define will have value `sig_atomic_t' or
+             `volatile sig_atomic_t' accordingly.])
+
+AC_MSG_CHECKING(for sig_atomic_t in signal.h)
+AC_EGREP_HEADER(sig_atomic_t,signal.h,
+  [
+    ac_cv_type_sig_atomic_t=yes;
+    AC_EGREP_HEADER(volatile.*sig_atomic_t,
+                    signal.h,
+                    [
+                        is_sig_atomic_t_volatile=yes;
+                        AC_MSG_RESULT([yes, volatile])
+                    ],
+                    [
+                        is_sig_atomic_t_volatile=no;
+                        AC_MSG_RESULT([yes, non volatile])
+                    ])
+  ],
+  [
+    AC_MSG_RESULT(no)
+    AC_CHECK_TYPE(sig_atomic_t, int)
+    is_sig_atomic_t_volatile=no
+  ])
+if test $is_sig_atomic_t_volatile = 'yes'
+then
+    AC_DEFINE(SIG_ATOMIC_VOLATILE_T, sig_atomic_t)
+else
+    AC_DEFINE(SIG_ATOMIC_VOLATILE_T, [volatile sig_atomic_t])
+fi
+
 
 dnl ############################################################################
 dnl Check for functions

lib/global.h

@@ -265,7 +265,7 @@ typedef struct
         gboolean alternate_plus_minus;
 
         /* Set if the window has changed it's size */
-        volatile sig_atomic_t winch_flag;
+        SIG_ATOMIC_VOLATILE_T winch_flag;
     } tty;
 
     struct

lib/tty/tty.c

@@ -62,7 +62,7 @@ int mc_tty_frm[MC_TTY_FRM_MAX];
 
 /*** file scope variables ************************************************************************/
 
-static volatile sig_atomic_t got_interrupt = 0;
+static SIG_ATOMIC_VOLATILE_T got_interrupt = 0;
 
 /*** file scope functions ************************************************************************/
 /* --------------------------------------------------------------------------------------------- */

lib/vfs/netutil.c

@@ -36,7 +36,7 @@
 
 /*** global variables ****************************************************************************/
 
-volatile sig_atomic_t got_sigpipe = 0;
+SIG_ATOMIC_VOLATILE_T got_sigpipe = 0;
 
 /*** file scope macro definitions ****************************************************************/
 

lib/vfs/netutil.h

@@ -16,7 +16,7 @@
 
 /*** global variables defined in .c file *********************************************************/
 
-extern volatile sig_atomic_t got_sigpipe;
+extern SIG_ATOMIC_VOLATILE_T got_sigpipe;
 
 /*** declarations of public functions ************************************************************/
 

src/execute.c

@@ -319,7 +319,7 @@ toggle_panels (void)
     vfs_path_t **new_dir_p;
 #endif /* ENABLE_SUBSHELL */
 
-    volatile sig_atomic_t was_sigwinch = 0;
+    SIG_ATOMIC_VOLATILE_T was_sigwinch = 0;
 
     channels_down ();
     disable_mouse ();