Link BLAS explicitly on non-Mac platforms

Fixes issue #3.
diff --git a/internal/ceres/CMakeLists.txt b/internal/ceres/CMakeLists.txt
index 1601666..f02db23 100644
--- a/internal/ceres/CMakeLists.txt
+++ b/internal/ceres/CMakeLists.txt
@@ -119,6 +119,12 @@
       ${METIS_LIB})
 ENDIF (EXISTS ${METIS_LIB})
 
+IF (EXISTS ${BLAS_LIB})
+  SET(CERES_LIBRARY_DEPENDENCIES
+      ${CERES_LIBRARY_DEPENDENCIES}
+      ${BLAS_LIB})
+ENDIF (EXISTS ${BLAS_LIB})
+
 IF (OPENMP_FOUND)
   SET(CERES_LIBRARY_DEPENDENCIES
     ${CERES_LIBRARY_DEPENDENCIES}