Improvements to fgetwln(3) from Andrey Chernov:

1) Set the stdio error indicator on __slbexpand() failure.

2) fgetwc(3) may succeed even when ferror(3) is already set
(for example, consider a program using SIG_IGN on SIGTTIN,
reading from the tty while in the background, getting EIO,
then coming to the foreground and reading again).
So do not force fgetwln(3) to fail in such a case either.
(Yes, the program should probably clearerr(3) before
reading again, but let's be nicer in case it forgets.)

missing _

From OpenBSD:
bugfix: when fgetwc(3) fails, fgetwln(3) must fail as well;

- ansify, knf.
- no functional changes

branches: 1.4.6;
Use a proper char */size_t pair in __sfileext to keep track of the line
buffer for fgetln and fgetwln. Simplifies code by dropping the INT_MAX
related logic. Drop conditionals around FREELB, free(NULL) is valid.

__getdelim works on strings up to SIZE_MAX - 2 and returns 0 on EOF.
getdelim works on strings up to SSIZE_MAX and returns -1 on EOF.
__fgetstr is now just a wrapper around __getdelim and ensures that
the buffer doesn't overflow the one provided by FILE.
__slbexpand is now static in fgetwln as it is the only consumer of that func.

sign-compare fix

Add the missing wide char support functions from freebsd.
XXX: long double support is missing until we get gdtoa, and add the
necessary wide functions.