Convert printed warning message to logged warning message.

theano/tensor/blas_headers.py

@@ -985,7 +985,7 @@ def blas_header_text():
 
 
 if not config.blas.ldflags:
-    print('Using NumPy C-API based implementation for BLAS functions.')
+    _logger.warning('Using NumPy C-API based implementation for BLAS functions.')
 
 
 def mkl_threads_text():