exec no longer available for app data folder in Android >= 10

[dna2github]

ref: termux/termux-app#1072

solutions:

• embedded proot, ref: https://github.com/termux/proot
• qemu, ref: https://github.com/limboemu/limbo

[dna2github]

ref: termux/termux-app@f6c3b6f