This ensures that only one set of includes is associated with each
object file, reagardless of where it's used.

For example, if apps/build.info has this:

    SOURCE[openssl]=foo.c
    INCLUDE[openssl]=.. ../include

and test/build.info has this:

    SOURCE[footest]=../apps/foo.c
    INCLUDE[footest]=../include

The inclusion directories used for apps/foo.o would differ depending
on which program's dependencies get generated first in the build file.

With this change, all those INCLUDEs get combined into one set of
inclusion directories tied to the object file.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5153)