I recently installed GHC 6.12 and the Haskell Platform 2010.1.0.1 on my Intel MacBook running OS X 10.5.8, and initially, everything worked fine. However, I discovered that if I use cabal install to install a package which depends on a MacPorts library (e.g., cabal install --extra-lib-dirs=/opt/local/lib --extra-include-dirs=/opt/local/include gd), things work fine in GHCi, but if I try to compile, I get the error

Linking test ...
Undefined symbols:
  "_iconv_close", referenced from:
      _hs_iconv_close in libHSbase-4.2.0.0.a(iconv.o)
  "_iconv", referenced from:
      _hs_iconv in libHSbase-4.2.0.0.a(iconv.o)
  "_iconv_open", referenced from:
      _hs_iconv_open in libHSbase-4.2.0.0.a(iconv.o)
ld: symbol(s) not found
collect2: ld returned 1 exit status

After some Googling, I found a long Haskell-cafe thread discussing this problem. The upshot seems to be that MacPorts installs an updated version of libiconv, and the binary interface is slightly different from the version included with the system. Consequently, if you try to link with any MacPorts library, the MacPorts libiconv gets linked in too; and since the base library was built to link against a different version of libiconv, things break. I've tried setting LD_LIBRARY_PATH and DYLD_LIBRARY_PATH and adding more flags to try to get it to look at /usr/lib again (e.g. cabal install --extra-lib-dirs=/opt/local/lib --extra-include-dirs=/opt/local/include --extra-lib-dirs=/usr/lib --extra-include-dirs=/usr/include gd), but neither worked. Uninstalling the MacPorts libiconv isn't really an option, since I have a bunch of ports installed which depend on it---including some ports I want Haskell to link to, like gd2.

From what I've seen online, the upshot really seems to be "you're boned": you cannot link against any MacPorts library while compiling with GHC, and there doesn't seem to be a solution. However, that thread was from the end of 2009, so I figure there's a chance that someone has a solution, workaround, ridiculous hack… anything, really. So: does anybody know how to get GHC 6.12 to link against the system libiconv at the same time as it links to libraries from MacPorts? Or, failing that, a way to make linking not break in some other clever way?