While that trick can be used for detecting if strict exists, it won't turn strict on.

            strict ends here
                   |
                   |
BEGIN {            v
   eval 'use strict';
   warn("Cannot 'use strict', it appears to be missing\n") if $@;
}
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On the other hand, the following works (and doesn't use eval EXPR):

BEGIN {           
   eval { require strict };
   if ($@) {
      warn("Cannot 'use strict', it appears to be missing\n");
   } else {
      strict->import();
   }
}
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