[GHC] #15968: configure doesn't error out when --enable-dwarf-unwind is given but libdw cannot be found

[GHC]

#15968: configure doesn't error out when --enable-dwarf-unwind is given but libdw
cannot be found
-------------------------------------+-------------------------------------
           Reporter:  nh2            |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.8.1
          Component:  Build System   |           Version:  8.6.2
  (make)                             |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Other
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Against expectations, the GHC bindist supposedly having DWARF support
 provided at

     https://downloads.haskell.org/~ghc/8.4.4/ghc-8.4.4-x86_64-deb9-linux-
 dwarf.tar.xz

 doesn't actually have DWARF support.

 According to bgamari, this is because `./configure --enable-dwarf-unwind`
 doesn't actually complain when the required dependency `libdw` isn't
 found; instead, it continues silently.

 Most programs I know will barf out when something isn't found but also
 *explicitly* requested via the command line; for the cases where this
 wasn't, the project maintainers did consider this a bug.

 GHC's `./configure` suite should fail hard when `--enable-dwarf-unwind` is
 given but `libdw` cannot be found.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15968>
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