Default clang target

[zorro]

Currently we are setting the llvm default target to $TERMUX_ARCH-unknown-linux-android24 which causes the __ANDROID_API__ to be set to 24 regardless of the device's API level. If we set default target to $TERMUX_ARCH-unknown-linux-android clang will use the __ANDROID_API__ value in the android/api-level.h header file. Then we could use a postinst script to change the __ANDROID_API__ value in the android/api-level.h header file to device's API level.

[finagolfin]

Good idea, but there was some code in the compiler itself that would behave differently based on the API level in the target and that couldn't use the default from our header if there was none in the target, so it defaults to a very large number. So despite other complaints like #6176, which I just saw, we have not done this and you can always specify the API level you want in your target yourself.

If you want to look into changing the defaults and see if it's feasible, I'd consider a pull for this.