Android: Fix build with NDK 27

NDK_PROC_*_ABI and NDK_ARCH_*_ABI were removed in the Android NDK 27 but will be reintroduced in the Android NDK 27b:

• https://github.com/android/ndk/issues/2049
• https://android-review.googlesource.com/c/platform/ndk/+/3196345

Both are only used when CMAKE_ANDROID_ARCH_ABI is NOT given. But currently the existence is also checked when CMAKE_ANDROID_ARCH_ABI is given. So we move the checks to the position they are required.

Backport: release
Topic-rename: android-ndk-27