Check for stdbool.h at configuration stage, and include it if available.

Check for lowercase 'bool' type at configuration stage. If not available
provide a suitable replacement with a type definition of 'unsigned char'
in setup_once.h

Move definitions of TRUE and FALSE to setup_once.h

setup_once.h

@@ -62,6 +62,10 @@
 #include <fcntl.h>
 #endif
 
+#ifdef HAVE_STDBOOL_H
+#include <stdbool.h>
+#endif
+
 
 /*
  * Definition of timeval struct for platforms that don't have it.
@@ -176,6 +180,28 @@ struct timeval {
                           (((unsigned char)x) == '\t'))
 
 
+/*
+ * Typedef to 'unsigned char' if bool is not an available 'typedefed' type.
+ */
+
+#ifndef HAVE_BOOL_T
+typedef unsigned char bool;
+#define HAVE_BOOL_T
+#endif
+
+
+/*
+ * Default definition of uppercase TRUE and FALSE.
+ */
+
+#ifndef TRUE
+#define TRUE 1
+#endif
+#ifndef FALSE
+#define FALSE 0
+#endif
+
+
 /*
  * Typedef to 'int' if sig_atomic_t is not an available 'typedefed' type.
  */