There was a transcription error in the comments in cstd.h for
the standard list of header files, where only the description
remained for <stdlib.h>, not the name of the file itself.
Remove several extraneous inclusions of the standard C99 headers.
Tested on the following afterwards:
Linux (using hints/linux.370) including tty, curses, qt6, and X11
macOS (using hints/macOS.370) including tty, curses, qt5, and X11
Windows MSYS2 using sys/windows/GNUmakefile
Windows Visual Studio using sys/windows/Makefile.nmake
msdos cross-compile on Ubuntu using djgpp cross-compiler
new .h files: hacklib.h selvar.h stairs.h
new .c files: calendar.c, getpos.c, report.c, selvar.c, stairs.c,
strutil.c, wizcmds.c
cleanup of hacklib.c and mdlib.c
hacklib contains functions that do not have to link with the core
relocate wiz commands from cmd.c to wizcmds.c
relocate CRASHREPORT stuff to report.c
relocate getpos stuff from do_name.c to getpos.c
remove temporary struct definition from extern.h
cross-compile PRE-section split into cross-pre1.370 and cross-pre2.370
Windows sys/windows/Makefile.nmake and sys/windows/Makefile.mingw32 and
visual studio project file updates
Unix sys/unix/Makefile.src, sys/unix/Makefile.utl
populate selvar.c and selvar.h
build on MS-DOS (not cross-compile) Makefile updates
for sys/msdos/Makefile.GCC (untested)
vms updates for above (untested)
