…es from the external libraries

terminfo/l/linux is now again installed on the emulator.

See libffi/libffi#265.
The external libraries are now untared in the build tree instead
of the source tree previously.

This is at Android build-tools version 25.0.3 and emulator version 26.0.3.

sys.prefix must not be located on /sdcard: pip adds a sys.prefix/bin/ directory
and fails upon PermissionError raised when using the /sdcard file system.