MacOS X 10.7.5 Lion. MacPro 4,1Intel dual CPU quad cores.
I've been away for a while so haven't worked on this. Back now and picking up the thread.

The bug is 13342 (see also 10015 and 10681) triggered by running
make check

bad return from expression `(f-sum -1 2000 -30000 40000000000)': expected 39999971999; got 39999972255
FAIL: test-ffi

There are 2 compilers available from Apple for C/C++ 
i686-apple-darwin11-llvm-gcc-4.2 (GCC) 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.1.00)
Apple clang version 3.0 (tags/Apple/clang-211.12) (based on LLVM 3.0svn)

I've built a standalone test with both of these compilers and they seem not to be the problem
Using the configure/make/make install is routine. But I am not familiar with the details of the make system.

I built guile-2.0.7 using the default configure/make and have 2 questions:
   (a) How can I find out which compiler/linker combo is used?
   (b) How can I change configure.ac to use the other one? (If that's the right place to make the change)

Thanks…

Peter