fix compilation bug.

theano/gof/cmodule.py

@@ -699,7 +699,8 @@ def gcc_module_compile_str(module_name, src_code, location=None, include_dirs=[]
         cmd.extend(p for p in preargs if not p.startswith('-O'))
     else:
         cmd.extend(preargs)
-    cmd.extend(config.gcc.cxxflags.split(' '))
+    if config.gcc.cxxflags:
+        cmd.extend(config.gcc.cxxflags.split(' '))
     cmd.extend('-I%s'%idir for idir in include_dirs)
     cmd.extend(['-o',lib_filename]) 
     cmd.append(cppfilename)