Build tweaks for ancient Macs

I don't expect anyone else to actually use ksh93 on a museum-grade
Power Mac G5 running Mac OS X 10.3.7, but ancient platforms are
great bug and compatibility testing tools. These tweaks restore the
ability to build on that platform.

Also, to avoid a strange path search bug on that platform and
possibly other ancient ones, set SHOPT_DYNAMIC to 0 in SHOPT.sh.

src/lib/libast/misc/debug.c

@@ -37,9 +37,12 @@ debug_fatal(const char* file, int line)
 	abort();
 }
 
-#if defined(_sys_times) && defined(_lib_getrusage)
+#if _sys_times && _lib_getrusage
 
 #include <times.h>
+#ifndef RUSAGE_SELF
+#include <sys/resource.h>
+#endif
 double
 debug_elapsed(int set)
 {