[openssl/openssl] b0bd7a: Use $config{build_file} instead of $target{build_f...

[Richard Levitte]

  Branch: refs/heads/openssl-3.1
  Home:   https://github.com/openssl/openssl
  Commit: b0bd7a28e8b4f6e9c2fcd7524b3803cd2f15e248
      https://github.com/openssl/openssl/commit/b0bd7a28e8b4f6e9c2fcd7524b3803cd2f15e248
  Author: Richard Levitte <levitte at openssl.org>
  Date:   2023-02-01 (Wed, 01 Feb 2023)

  Changed paths:
    M Configure
    M INSTALL.md
    M configdata.pm.in

  Log Message:
  -----------
  Use $config{build_file} instead of $target{build_file}

If the user specifies an alternative build file than the default, this
alternative is recorded in $config{build_file}, not $target{build_file}.
Therefore, the former should be used, leaving the latter as a mere default.

This is a bug.  While fixing it, document it better too.

Reviewed-by: Matt Caswell <matt at openssl.org>
Reviewed-by: Tomas Mraz <tomas at openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20173)

(cherry picked from commit aa2d7e0ee15d1b7015479c38f370a25ceec690fc)