Remove redundant null check before free. it is safe to free(NULL)
While here, clear up odd whitespace issue. NFC

PR/45989: Martin Husemann: lint invocation does include -w only on i386

- turn lint -w for all the platforms after fixing the lint warnings.
- add _DIAGASSERTS() for casts that would assign values to types that
would not fit.
- change types, add casts
- change into ansii prototypes
- turn on _DIAGNOSTIC for libc (during current, to be eliminated for release
builds)

approved by core@

branches: 1.3.2;
Make cp -p and mv preverve extended attributes, and complain if they cannot.

Also introduce library functions for copying extended attributes from one
file to another:
- extattr_copy_file, extattr_copy_fd, extattr_copy_link, with FreeBSD style,
where a namespace is to be supplied
- cpxattr, fcpxattr, lcpxattr, with Linux style, where all namespaces
accessible to the caller are copied, and the others are silently ignored.

A little libc namespace housekeeping exercise:
* Make vfprintf_unlocked() an internal function, c.f. __svfscanf_unlocked().
* Add internal names for arc4random(), endnetpath(), fhstatvfs(),
fstatvfs(), mkstemp(), shquote(), statvfs(), taddr2uaddr(), uaddr2taddr(),
uuid_create_nil(), uuid_is_nil(), and wcwidth().
* Include namespace.h where supposed to.

System calls and support routines for file system extended attributes. Libc
version is bumped to 12.125.

From FreeBSD.