Redo l10n support in the strerror family.

Instead of opening the message catelog whenever strerror is called,
keep track of the translations in the locale cache. For the C locale,
the builtin sys_errlist is used directly. Other locales will open
the catalog file on the first strerror call and build a translation
table, so that further calls in this locale can just use an array
lookup.

Arrange that strerror(-1) prints "Unknown error: -1" and not the
unsigned equivalent of -1.

While here, guarantee, even when !NLS, that nothing here (not even
snprintf deciding to complain about EILSEQ or something) can ever
alter errno (ie: always save and restore it, not only in the NLS case).
The functions here must never alter errno, whatever happens.

branches: 1.4.14;
PR/51814: Ngie Cooper: add <stdio.h> since sys_nerr is declared there on
FreeBSD.

branches: 1.3.8;
Add strerror_l.

branches: 1.2.44; 1.2.50;
- Fix the remaining indr_references so that they define lint symbols.
- Add an internal symbol for strerror_r (thanks klaus for noticing)
- Remove internal __strerror

PR/30845: Luke Mewburn: strerror_r(3) missing
- Merge 4.4BSD strerror.3 man page changes that summarize information
for all the error printing functions. This makes the perror(3) page
obsolete.
- Implement all error functions in terms of strerror_r(), including
__strerror() which is not used internally. Can it be removed?
- Bump version for strerror_r

Arrange that strerror(-1) prints "Unknown error: -1" and not the
unsigned equivalent of -1.

While here, guarantee, even when !NLS, that nothing here (not even
snprintf deciding to complain about EILSEQ or something) can ever
alter errno (ie: always save and restore it, not only in the NLS case).
The functions here must never alter errno, whatever happens.

PR/51814: Ngie Cooper: add <stdio.h> since sys_nerr is declared there on
FreeBSD.

branches: 1.3.8;
Add strerror_l.

branches: 1.2.44; 1.2.50;
- Fix the remaining indr_references so that they define lint symbols.
- Add an internal symbol for strerror_r (thanks klaus for noticing)
- Remove internal __strerror

PR/30845: Luke Mewburn: strerror_r(3) missing
- Merge 4.4BSD strerror.3 man page changes that summarize information
for all the error printing functions. This makes the perror(3) page
obsolete.
- Implement all error functions in terms of strerror_r(), including
__strerror() which is not used internally. Can it be removed?
- Bump version for strerror_r