Trouble linking Fortran libraries

I'm trying to use the IMSL Numerical Libraries (which are in Fortran) from an Objective-C++ program. I understand the source-level implications, but I'm having trouble at the linking phase. I've included the libimsl.a library in my Xcode project and confirmed that it is listed in the "Link Binaries with Libraries" build phase. But when I build, I get a number of "undefined symbols" errors. The first couple of which are:

"_imach_", referenced from:
_e6csf_ in libimsl.a(e6csf.o)
"__absoft_aint", referenced from:
_e6csf_ in libimsl.a(e6csf.o)​

Does anyone have any tips for linking Fortran libraries in Xcode?