2.4 Writing Guile Extensions Example - Mac Build Problem

[Roger Mc Murtrie]

I have just started learning Guile on my Mac OS X 10.10 (Yosemite) but my 
attempt to build the Writing Guile Extensions example failed with:

gcc `pkg-config --cflags guile-2.0` -shared -o libguile-bessel.so -fPIC bessel.c
Undefined symbols for architecture x86_64:
  "_scm_c_define_gsubr", referenced from:
      _init_bessel in bessel-6d66cf.o
  "_scm_from_double", referenced from:
      _j0_wrapper in bessel-6d66cf.o
  "_scm_to_double", referenced from:
      _j0_wrapper in bessel-6d66cf.o
ld: symbol(s) not found for architecture x86_64

The simple-guile example built and worked OK.

Any advice appreciated.