Configure: try to make sure every config target name is unique

Configurations of OpenSSL target platforms

==========================================

Target configurations are a collection of facts that we know about

Configuration targets are a collection of facts that we know about

different platforms and their capabilities.  We organise them in a

hash table, where each entry represent a specific target.

Note that configuration target names must be unique across all config

files.  The Configure script does check that a config file doesn't

have config targets that shadow config targets from other files.

In each table entry, the following keys are significant:

        inherit_from    => Other targets to inherit values from.

	%targets = read_eval_file($fname);

    }

    my %preexisting = ();

    foreach (sort keys %targets) {

        $preexisting{$_} = 1 if $table{$_};

    }

    die <<"EOF",

The following config targets from $fname

shadow pre-existing config targets with the same name:

EOF

        map { "  $_\n" } sort keys %preexisting

        if %preexisting;

    # For each target, check that it's configured with a hash table.

    foreach (keys %targets) {