Added Darwin 8.0 specific headers.

diff --git a/configure.ac b/configure.ac
index d60ebe1..bb55fad 100644
--- a/configure.ac
+++ b/configure.ac
@@ -188,7 +188,9 @@
 	linux/param.h \
 	linux/serial.h \
 	linux/ucdrom.h \
+	mach/machine.h \
 	machine/cpu.h \
+	machine/limits.h \
 	mntent.h \
 	netdb.h \
 	netinet/in.h \