libreplace: properly execute SYS_copy_file_range check

Closed Ralph Böhme requested to merge samba-team/devel/samba:slow-copy_file_range into master

It seems some systems (like Centos 7) have the SYS_copy_file_range define but fail the syscall when actually being called. The current configure check is only compiled, not run so erroneously reports a working SYS_copy_file_range.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14786

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