chore: release v0.2.168

(backport <#4191>)
(cherry picked from commit 65d0ffb)

[ref](https://man.freebsd.org/cgi/man.cgi?query=tcp)

(backport <#4193>)
(cherry picked from commit abf49f6)

(backport <#4194>)
(cherry picked from commit 816a236)

(backport <#4195>)
(cherry picked from commit c66faeb)

Create a module providing the same definitions of `c_char` as in
`rust-lang/rust`, which in most cases are based on the architecture
rather than the OS. This will allow individual platforms to reexport the
definition rather than having configuration repeated in numerous
modules.

(backport <#4198>)
(cherry picked from commit 28d4064)

- aarch64-kmc-solid_asp3
- armv7a-kmc-solid_asp3-eabi
- armv7a-kmc-solid_asp3-eabihf
- riscv64-linux-android
- x86_64-unknown-l4re-uclibc
- armv7-sony-vita-newlibeabihf
- riscv32imac-unknown-nuttx-elf
- riscv32imafc-unknown-nuttx-elf
- riscv32imc-unknown-nuttx-elf
- riscv64gc-unknown-nuttx-elf
- riscv64imac-unknown-nuttx-elf
- thumbv6m-nuttx-eabi
- thumbv7em-nuttx-eabi
- thumbv7em-nuttx-eabihf
- thumbv7m-nuttx-eabi
- thumbv8m.base-nuttx-eabi
- thumbv8m.main-nuttx-eabi
- thumbv8m.main-nuttx-eabihf
- aarch64-unknown-redox
- aarch64-unknown-illumos
- riscv32-wrs-vxworks
- riscv64-wrs-vxworks

(backport <#4199>)
(cherry picked from commit 0344a78)

(backport <#4200>)
(cherry picked from commit c389c30)

(backport <#4205>)
(cherry picked from commit c33744e)

For any platforms that have `c_char` within a `cfg_if` block, ensure
they match the top-level `arch` definitions and reexport that to clean
up code.

(backport <#4205>)
(cherry picked from commit fead383)

[0.2] Backports

Fixes #4209

(backport <#4210>)
(cherry picked from commit 9ff3409)

[0.2] Skip `c_char_def` on OpenBSD

Co-authored-by: Trevor Gross <tmgross@umich.edu>