This variant will be more interoperable across various systems
and it's already used in Ruby module.

Otherwise, configure tests fail on NetBSD with:

  gcc: Missing argument for -Wl,-rpath

Now it's possible to disable default bind mounts of
languages by setting:

  {
      "isolation": {
           "automount": {
               "language_deps": false
           }
     }
  }

In this case, the user is responsible to provide a "rootfs"
containing the language libraries and required files for
the application.

Some PPAs for Ubuntu package PHP with versions like:
 7.2.28-3+ubuntu18.04.1+deb.sury.org+1

But the script expected only "X.Y.Z".

The issue was introduced in:
 http://hg.nginx.org/unit/rev/2ecb15904ba5

Now it prints version even if PHP was built without embed SAPI.

For each request, the worker calls the php_execute_script function
from libphp that changes to the script directory before doing its
work and then restores the process directory before returning.  The
chdir(2) calls it performs are unnecessary in Unit design.  In simple
benchmarks, profiling shows that the chdir syscall code path (syscall,
FS walk, etc.) is where the CPU spends most of its time.

PHP SAPI semantics requires the script to be run from the script
directory.  In Unit's PHP implementation, we have two use cases:

- script
- arbitrary path

The "script" configuration doesn't have much need for a working
directory change: it can be changed once at module initialization.
The module needs to chdir again only if the user's PHP script also
calls chdir to switch to another directory during execution.

If "script" is not used in Unit configuration, we must ensure the
script is run from its directory (thus calling chdir before exec),
but there's no need to restore the working directory later.

Our implementation disables mandatory chdir calls with the SAPI
option SAPI_OPTION_NO_CHDIR, instead calling chdir only when needed.

To detect the user's calls to chdir, a simple "unit" extension is
added that hooks the built-in chdir() PHP call.

Currently almost all Unit object files depends on generated nxt_version.h.
This patch adds missing dependence and fixes running make with multiple
jobs.

This closes #318 issue on GitHub.