[opendx-dev] Changes to memory.c

[Rick Scott]

The latest changes to memory.c prevent me from building. It seems that I don't
have sys/sysinfo.h. Instead I need linux/kernel.h and linux/sys.h in order to
use the sysinfo function, according to my man pages. Also, using an #if linux
is almost the same as #if computer. There is _so_ much variation with linux
systems that it is almost a useless check. Instead you should be doing a
configure check for the functionality you want. In this case an
AC_CHECK_HEADER(sys/sysinfo.h).