Make recursion_check work for multiple threads

With multiple threads, using an unprotected static variable to check
whether recursion has occured isn't valid, as one thread might have
modified the variable, thus causing another thread to incorrectly
conclude that recursion has occured.  This patch avoids this problem
by using a thread-specific variable for the recursion check.

Regtested on x86_64-pc-linux-gnu.

libgfortran/ChangeLog:

2018-11-23  Janne Blomqvist  <jb@gcc.gnu.org>

	* runtime/error.c (MAGIC): Remove.
	(recursion_key): New variable.
	(recursion_check): Use thread-specific variable for recursion
	check if threads are active.
	(constructor_recursion_check): New function.
	(destructor_recursion_check): New funcion.

From-SVN: r266419

libgfortran/ChangeLog

+2018-11-23  Janne Blomqvist  <jb@gcc.gnu.org>
+
+	* runtime/error.c (MAGIC): Remove.
+	(recursion_key): New variable.
+	(recursion_check): Use thread-specific variable for recursion
+	check if threads are active.
+	(constructor_recursion_check): New function.
+	(destructor_recursion_check): New funcion.
+
 2018-11-22  Janne Blomqvist  <jb@gcc.gnu.org>
 
 	* acinclude.m4 (LIBGFOR_CHECK_ATOMIC_FETCH_ADD): Rename and test

libgfortran/runtime/error.c

@@ -332,21 +332,50 @@ show_locus (st_parameter_common *cmp)
 
 /* recursion_check()-- It's possible for additional errors to occur
  * during fatal error processing.  We detect this condition here and
- * exit with code 4 immediately. */
+ * abort immediately. */
 
-#define MAGIC 0x20DE8101
+static __gthread_key_t recursion_key;
 
 static void
 recursion_check (void)
 {
-  static int magic = 0;
+  if (__gthread_active_p ())
+    {
+      bool* p = __gthread_getspecific (recursion_key);
+      if (!p)
+        {
+          p = xcalloc (1, sizeof (bool));
+          __gthread_setspecific (recursion_key, p);
+        }
+      if (*p)
+	sys_abort ();
+      *p = true;
+    }
+  else
+    {
+      static bool recur;
+      if (recur)
+	sys_abort ();
+      recur = true;
+    }
+}
 
-  /* Don't even try to print something at this point */
-  if (magic == MAGIC)
-    sys_abort ();
+#ifdef __GTHREADS
+static void __attribute__((constructor))
+constructor_recursion_check (void)
+{
+  if (__gthread_active_p ())
+    __gthread_key_create (&recursion_key, &free);
+}
 
-  magic = MAGIC;
+static void __attribute__((destructor))
+destructor_recursion_check (void)
+{
+  if (__gthread_active_p ())
+    __gthread_key_delete (recursion_key);
 }
+#endif
+
 
 
 #define STRERR_MAXSZ 256