Spurious undefined reference to `openpty'

I'm seeing these since upgrading our build machines from Ubuntu 10.04 to 12.04:

=====> process001(dyn) 3159 of 3394 [0, 96, 0]
cd ../../libraries/process/tests && '/64playpen/simonmar/nightly/HEAD-cam-04-unx/x86_64-unknown-linux/inplace/bin/ghc-stage2' -fforce-recomp -dcore-lint -dcmm-lint -dno-debug-output -no-user-package-db -rtsopts  -fno-ghci-history -o process001 process001.hs -O -dynamic   >process001.comp.stderr 2>&1
Compile failed (status 256) errors were:
[1 of 1] Compiling Main             ( process001.hs, process001.o )
Linking process001 ...
/64playpen/simonmar/nightly/HEAD-cam-04-unx/x86_64-unknown-linux/libraries/unix/dist-install/build/libHSunix-2.5.1.0-ghc7.5.20120706.so: undefined reference to `openpty'
collect2: ld returned 1 exit status

*** unexpected failure for process001(dyn)

I'm stumped. Here's what I've discovered so far:

• It only happens with -dynamic
• The openpty symbol comes from the util library, which we are correctly linking in. The libutil.so library is present, and I've checked that we're getting the right one.
• It only happens when using the process package, which depends on unix. Using unix by itself is fine. So something about the process package is messing up the linker.
• I've tried removing all the -L options and linking libraries by full pathname, just in case we're picking up something from the wrong place; that doesn't help.

Trac metadata

Trac field	Value
Version	7.4.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	high
Resolution	Unresolved
Component	Compiler
Test case
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