Using libandroid-shmem in proot/chroot environment.

[twaik]

It is possible to use libandroid-shmem inside proot/chroot distros to improve performance of programs and to improve communicating of termux programs with programs in proot/chroot.

To make this possible you should make using linux/ashmem.h optional by embedding needed macros into shmem.c and making DBG macro empty if __ANDROID__ is not defined.

Also it is possible to generate installable library automatically by creating Github Action which cross-compiles library for all popular architectures. It would be better to make script which installs library for needed architecture and writes /etc/ld.preload script. To not confuse people with different architectures and different package systems I recommend generating single file script with built-in libraries encoded as base64 strings. This script can be published with Github Releases.

I can make pull request if you tell it is needed.

Related to #2, #3, #5, #6, #7.