Explicitly define SUNOS4 for SunOS 4.1.x builds instead of hiding it in the Tinderbox script.

configure.in

@@ -626,6 +626,7 @@ dnl the qsort routine under solaris is faulty
     DSO_LDOPTS='-Bdynamic'
     MKSHLIB='-$(LD) $(DSO_LDOPTS)'
     MKCSHLIB='-$(LD) $(DSO_LDOPTS)'
+    AC_DEFINE(SUNOS4)
     AC_DEFINE(SPRINTF_RETURNS_STRING)
     ;;