Fix OHOS define

[jschwe]

Extracted from #583.

target_is_ohos was not working as expected. This presumably originated in a seemingly harmless suggestion,
but surprisingly the expected return type / values for these functions is True | None, and not True | False (The other functions like target_is_xx don't return anything explicitly if the if does not match, which results in a None implicitly I guess). Returning False does not give the expected result. I noticed this while working on #583 - normally logs are still visible in servo, since we setup a thread that redirects output from stdout / stderr to the logging system on ohos (except in production mode).

Fixing the ohos define also revealed some issues with the patches:

• In the current version of SM, LogLevel defined in hilog/log.h collides with a LogLevel in the js namespace. Some of the header files we included hilog in, have this collision, and are also used from C files, so we can't just namespace the import (without the patch getting quite ugly).To avoid these issues we just copy the function declaration, and use raw integers instead of the enum in the function signature.

[jschwe]

Todo: add ci configuration for ohos with debugmozjs
Edit: done

[jschwe]

This PR did change a bit since the initial review, so it might make sense to be reviewed again. I'm not super happy with inlining the function declaration in every file it is used, but I don't think it would make the patching easier, if I wrapped the logging in a new header file.

[jdm]

That's fair.