whisper.android : fix cmake multiple libraries build

[jhen0409]

After #1204, the Android build will only generate two shared libraries which it breaks the previous ABI compatibility:

$ $ANDROID_HOME/cmdline-tools/latest/bin/apkanalyzer files list \
  ~/workspace/whisper.cpp/examples/whisper.android/app/build/outputs/apk/debug/app-debug.apk \
  | grep libwhisper

/lib/armeabi-v7a/libwhisper_vfpv4.so
/lib/arm64-v8a/libwhisper_v8fp16_va.so

After this PR, we can see these are restored:

/lib/x86_64/libwhisper.so
/lib/x86/libwhisper.so
/lib/armeabi-v7a/libwhisper_vfpv4.so
/lib/armeabi-v7a/libwhisper.so
/lib/arm64-v8a/libwhisper_v8fp16_va.so
/lib/arm64-v8a/libwhisper.so