scandir,readdir[_t]: use one common source for X() and X64()

scandir,readdir[_t]: use one common source for X() and X64()

Since the sources differ only minimally, use only scandir.c,readdir[_t].c
and redefine the used functions accordingly.
Use a strong_alias instead of compiling *64.c if __WORDSIZE = 64

Signed-off-by: Peter S. Mazinger <ps.m@gmx.net>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>