configure: support --extra-ldflags

[pirDOL]

Add --extra-ldflags to configure for static link libaio.

Please confirm that your commit message(s) follow these guidelines:

1. First line is a commit title, a descriptive one-liner for the change
2. Empty second line
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Reminders:

1. If you modify struct thread_options, also make corresponding changes in
   cconv.c and bump FIO_SERVER_VER in server.h
2. If you change the ioengine interface (hooks, flags, etc), remember to bump
   FIO_IOOPS_VERSION in ioengines.h.

[vincentkfu]

Please update the Signed-off-by tag use your real name.

[pirDOL]

Please update the Signed-off-by tag use your real name.

[pirDOL]

Please update the Signed-off-by tag use your real name.

done