[tor-bugs] #21023 [Core Tor/Tor]: Replace custom checks with Autoconf macros

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#21023: Replace custom checks with Autoconf macros
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 Reporter:  cypherpunks   |          Owner:
     Type:  defect        |         Status:  new
 Priority:  Medium        |      Milestone:  Tor: unspecified
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:                |  Actual Points:
Parent ID:                |         Points:
 Reviewer:                |        Sponsor:
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Comment (by cypherpunks):

 Actually `AC_CHECK_DECLS` should be used instead of `AC_CHECK_DECL`
 because it defines `HAVE_DECL_symbol` for us.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21023#comment:1>
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