What is the permission ACCESS_WEATHERCLOCK_PROVIDER?

Andrew's guess was correct: According to Android Census, this permission is declared by Huawei's own weather app (or rather the data provider behind it). The site further shows it has been found on Huawei devices only (at least by them), covered by different protection levels (ranging from "normal" to "signature|system"), thus it cannot be even clearly said whether its declaration by some user app would have any effect at all.

For clarification: com.huawei.android.weather is a Content Provider, protecting access to its data via the android.permission.ACCESS_WEATHERCLOCK_PROVIDER. If an app requests that permission, it must be granted to it on install – which is done based on at least two conditions to be met: 1) Android knows of that permission (i.e. the app providing it is already installed), and 2) the protection level permits it. For "user-installed apps" that limits it to "normal" and "dangerous" protection levels. Now note the second census link: for some devices, this permission uses level "normal" (so it's available to user-apps), while on others it is "system|signature" (and thus not available to user-apps).