from: http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/Tutorials/pdf/packages/SPICE_Tutorials_Merged.pdf

The default SPICE library names do not conform to the UNIX 
convention libname.a. So you cannot use the conventional 
library path/name options –L and –l, e.g. 
 gcc … -L/path_to_libs/ -lname 
 unless you rename the SPICE library.

I imagine renaming both .a files is the better course of action rather than symlinking them both?