These are defined in the fcntl.h glibc header on MIPS systems
on Linux but missing in the libc crate, so add them as they are
required for the file locking API in rustc.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

Discovered while debugging: djg/audioipc-2#52

These errno's are defined in <sys/errno.h> on DragonFlyBSD.

Signed-off-by: Levente Kurusa <lkurusa@acm.org>

Signed-off-by: Gerd Zellweger <gzellweger@vmware.com>

Closes #1060 .

Signed-off-by: Gerd Zellweger <mail@gerdzellweger.com>

This used to be defined multiple times in different (but not all)
architectures. Moving it to general linux module since it's an
architecture independent feature.

This commit prepares the `libc` crate to be included directly into the
standard library via crates.io. More details about this can be found on
rust-lang/rust#56092, but the main idea is that this crate now depends
on core/compiler-builtins explicitly (but off-by-default).

The main caveat here is that this activates `no_core` when building as
part of libstd, which means that it needs to explicitly have an `iter`
and `option` module for the expansion of `for` loops to work.

unix::uclibc::mips has both support for mips and mips64, but it's
currently only imported for mips.