alloca.c, [...]: Improve manual formatting.

	* alloca.c, clock.c, getcwd.c, getpagesize.c, getpwd.c, index.c,
	libiberty.texi, memchr.c, putenv.c, rindex.c, strchr.c, strdup.c,
	strerror.c, strrchr.c, strstr.c, strtod.c, tmpnam.c, vfork.c,
	xatexit.c, xmalloc.c, xstrerror.c: Improve manual formatting.  Fix
	spelling.  Give names to function arguments in documentation.  Use
	(void) prototypes in documentation.
	* functions.texi: Regenerate.

From-SVN: r46068