[libcxx] Add OHOS support

[kpdev42]

Summary

Add support for OpenHarmony OS (OHOS)

OpenHarmony is an open-source project incubated and operated by the OpenAtom Foundation. It targets IoT, and already used on production devices.

General OpenHarmony OS discussion on discourse thread: "Add support for OpenHarmony OS"

LLVM and clang parts of OHOS support: D138202, D145227

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Huawei RRI, OS Lab

[philnik]

As usual: Do you plan to get official support for OpenHarmony in libc++? If that's the case, please take a look at https://libcxx.llvm.org/AddingNewCIJobs.html#addingnewcijobs.

[Mordante]

Can you update the commit message to explain what OHOS is and provide a link to its homepage. That would be nice to have as a future reference.

[thesamesam]

The atomic changes look fine.

[kpdev42]

In D146804#4219942, @Mordante wrote:

Can you update the commit message to explain what OHOS is and provide a link to its homepage. That would be nice to have as a future reference.

Description is updated, please take a look

[kpdev42]

In D146804#4219175, @philnik wrote:

As usual: Do you plan to get official support for OpenHarmony in libc++? If that's the case, please take a look at https://libcxx.llvm.org/AddingNewCIJobs.html#addingnewcijobs.

Sure, we will try it, thank you

[Mordante]

In D146804#4248520, @kpdev42 wrote:

In D146804#4219175, @philnik wrote:

As usual: Do you plan to get official support for OpenHarmony in libc++? If that's the case, please take a look at https://libcxx.llvm.org/AddingNewCIJobs.html#addingnewcijobs.

Sure, we will try it, thank you

That would indeed be great to have.

LGTM, modulo one remark.

libcxx/include/__locale

46

At least I assume that was intended.