Fix alignment tests for ARM on Linux. #14848
rustc: Link entire archives of native libraries

As discovered in #15460, a particular #[link(kind = "static", ...)] line is not
actually guaranteed to link the library at all. The reason for this is that if
the external library doesn't have any referenced symbols in the object generated
by rustc, the entire library is dropped by the linker.

For dynamic native libraries, this is solved by passing -lfoo for all downstream
compilations unconditionally. For static libraries in rlibs this is solved
because the entire archive is bundled in the rlib. The only situation in which
this was a problem was when a static native library was linked to a rust dynamic
library.

This commit brings the behavior of dylibs in line with rlibs by passing the
--whole-archive flag to the linker when linking native libraries. On OSX, this
uses the -force_load flag. This flag ensures that the entire archive is
considered candidate for being linked into the final dynamic library.

This is a breaking change because if any static library is included twice in the
same compilation unit then the linker will start emitting errors about duplicate
definitions now. The fix for this would involve only statically linking to a
library once.

Closes #15460
[breaking-change]
Change everything returning `libc::sockaddr_storage` to use an &mut out-ptr instead

The BSD socket code does some cast tricks with the `libc::sockaddr*`
structs, which causes useful data to be stored in struct padding.
Since Load/Store instructions do not copy struct padding, this makes
these structures dangerous to pass or return by value.

In particular, https://github.com/rust-lang/rust/issues/15763 changes
return semantics so that a Load instruction is used, breaking the TCP
code. Once this PR is merged, that one should merge without error.
auto merge of #16251 : apoelstra/rust/tcp-fix, r=alexcrichton

Replacement for PR #16208 (make sockaddr* struct padding explicit) to make PR #15763 (fix nested returns) merge without breaking TCP code.
auto merge of #16110 : alexcrichton/rust/issue-15460, r=brson

As discovered in #15460, a particular #[link(kind = "static", ...)] line is not
actually guaranteed to link the library at all. The reason for this is that if
the external library doesn't have any referenced symbols in the object generated
by rustc, the entire library is dropped by the linker.

For dynamic native libraries, this is solved by passing -lfoo for all downstream
compilations unconditionally. For static libraries in rlibs this is solved
because the entire archive is bundled in the rlib. The only situation in which
this was a problem was when a static native library was linked to a rust dynamic
library.

This commit brings the behavior of dylibs in line with rlibs by passing the
--whole-archive flag to the linker when linking native libraries. On OSX, this
uses the -force_load flag. This flag ensures that the entire archive is
considered candidate for being linked into the final dynamic library.

This is a breaking change because if any static library is included twice in the
same compilation unit then the linker will start emitting errors about duplicate
definitions now. The fix for this would involve only statically linking to a
library once.

Closes #15460
[breaking-change]
auto merge of #16179 : SimonPersson/rust/master, r=brson

This should solve issue 14848 for ARM.