I can reproduce essentially the same error on Win32. It seems to be caused by the line (in the top level Makefile.PL):

'MYEXTLIB'        => 'mylib/libmylib$(LIB_EXT)',
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But I don't know much more than that at this stage. (That line fits quite well with the MYEXTLIB documentation, though I do recall having found MYEXTLIB to not quite work as advertised on previous occasions.) Someone else might be able to chip in with a solution - otherwise I'll take a closer look when time permits.

Cheers,
Rob