Remove or replace non-portable headers

[hermabe]

These are the headers I could find:

Header	About	Used in
dirent.h	POSIX header, directories	xd.c
dlfcn.h	POSIX header, dynamic linking	jconsole.c, jeload.cpp, jfex.c, x15.c, xf.c
fcntl.h	POSIX header, file control	xf.c
fts.h	GNUlib header, file hierarchy traversal	xf.c
mach-o/dyld.h	Mac dynamic library	jeload.cpp
spawn.h	POSIX header (ADVANCED REALTIME)	xh.c
sys/mman.h	POSIX header, memory management	io.c
sys/resource.h	POSIX header, XSI resource operations	jconsole.c
sys/stat.h	POSIX header, file attributes	xd.c, xf.c
sys/time.h	POSIX header, time types	xt.c
sys/types.h	POSIX header, data types	xf.c
sys/utsname.h	POSIX header, name and info about kernel	jeload.cpp
sys/wait.h	POSIX header, waiting	xh.c
unistd.h	POSIX header, standard symbolic constants and types	io.c, jconsole.c, xd.c, xf.c, xh.c, xl.c, xt.c

Most of these are used in either foreigns or dynamic library loading

[Sebanisu]

I think some of this should happen overtime when we replace code with things from the c++ standard library. Though it's nice to know about these things. :)