Use "android-xx" format for ANDROID_PLATFORM

[DDoSolitary]

Changelog: Bugfix: Use "android-" format for the ANDROID_PLATFORM argument to be compatible with old NDK versions.
Docs: omit

Closes: #11798

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Fixes #11798

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[franramirez688]

Hi @DDoSolitary

Thanks for your contribution! The PR looks good! One point about it, let me add a little check in our tests to verify that we're setting the variable correctly. Let me know if you have any other doubt.

[memsharded]

Android is not sufficiently tested in our CI.
Are we completely sure that this format android-xxx does not break for more modern API levels? It is compatible for all current (and hopefully future) levels?

[franramirez688]

As far as it's shown in the official documentation, https://developer.android.com/ndk/guides/cmake?hl=es-419#android_platform is not saying anything about "restrictions" in terms of using android-xxx for modern versions, so it should work as usual.

From official docs:

Multiple formats are accepted for this parameter:

* android-$API_LEVEL
* $API_LEVEL
* android-$API_LETTER

The $API_LETTER format allows you to specify android-N without the need to determine the number associated with that release. Note that some releases received an API increase without a letter increase. These APIs can be specified by appending the -MR1 suffix. For example, API level 25 is android-N-MR1.