SIO-1126 Make compilation isolated: PRootExecutor

PRootExecutor works like chroot + mount --bind and is based on ptrace.

New sandbox `proot-sandbox` is necessary in order to use it.
Default fpc was upgraded to 2.4.4 due to incompatibility of previous
version.

Change-Id: I2b65bb7f910119272c9824d31b89609833137041