DSO linking bug in unix package

unix depends on libpthread, but it's not listed under extra-libraries in the cabal file. For that reason some programs fail to build on Ubuntu 13.04.

Steps to reproduce:

-- Main.hs
import System.Posix.Semaphore

main :: IO ()
main = do
  semUnlink "foo"

$ ghc --make Main.hs

Expected result: Program is compiled and linked.

Actual result: Liking fails with

/usr/bin/ld: /home/foo/.install/haskell/ghc-7.6.2/lib/ghc-7.6.2/unix-2.6.0.1/libHSunix-2.6.0.1.a(Semaphore__5.o): undefined reference to symbol 'sem_unlink@@GLIBC_2.2.5'
/usr/bin/ld: note: 'sem_unlink@@GLIBC_2.2.5' is defined in DSO /lib/x86_64-linux-gnu/libpthread.so.0 so try adding it to the linker command line
/lib/x86_64-linux-gnu/libpthread.so.0: could not read symbols: Invalid operation
collect2: error: ld returned 1 exit status

This is related to https://fedoraproject.org/wiki/UnderstandingDSOLinkChange.

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/unix
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