Do not link boost numpy library if python is disabled.

Author: tskisner

src/libharp/math/Makefile.am

@@ -25,8 +25,11 @@ noinst_LTLIBRARIES = libharpmath.la
 libharpmath_la_includedir = $(includedir)/harp
 libharpmath_la_include_HEADERS = harp/math.hpp harp/linalg.hpp
 libharpmath_la_SOURCES = harp_linalg.cpp harp_math.cpp
-libharpmath_la_LIBADD = \
-$(top_builddir)/src/libharp/math/boost_numpy/libboost_numpy.la
+libharpmath_la_LIBADD = 
+
+if HAVE_AM_PYTHON
+  libharpmath_la_LIBADD += $(top_builddir)/src/libharp/math/boost_numpy/libboost_numpy.la
+endif
 
 install-data-local:
 	@$(mkinstalldirs) $(DESTDIR)$(includedir)/boost; \