Previously, NGX_MACHINE was not set when crossbuilding, resulting in
NGX_ALIGNMENT=16 being used in 32-bit builds (if not explicitly set to a
correct value).  This in turn might result in memory corruption in
ngx_palloc() (as there are no usable aligned allocator on Windows, and
normal malloc() is used instead, which provides 8 byte alignment on
32-bit platforms).

To fix this, now i386 machine is set when crossbuilding, so nginx won't
assume strict alignment requirements.

When installing or running from a non-root user it is sometimes required to
override default, compiled in error log path. There was no way to do this
without rebuilding the binary (ticket #147).

This patch introduced "-e" command line option which allows one to override
compiled in error log path.

Signed-off-by: Piotr Sikora <piotr@cloudflare.com>

If set, its value is output in "nginx -v" and in the error log.

Otherwise, we may fail to properly detect a version of compiler.