work around a bug in musl w.r.t to O_SEARCH and use EIO_O_PATH instead, vertifying the semantics against the subset of O_PATH and O_SEARCH (based on a report by Steve Dondley). aio_copy now tries to preallocate the destination file. fexecve configure test used the wrong püointer type (patch by Paul Howarth).
![IO-AIO-4.81](https://cdn-ak-scissors.b.st-hatena.com/image/square/c4a607b5430575638fd9a7f233e073d867af4bb7/height=288;version=1;width=512/https%3A%2F%2Fmetacpan.org%2Fstatic%2Fimages%2Fdots.png)