inserting missing comma when adding '-ccbin' to direct argument flags

@betatim provided a fix to Theano/Theano#1912 in commit Theano/Theano@bb4b1a5.  However, that fix did not include a comma on the end of the line, causing the `'-ccflags'` to be merged with the next string `'--fmad'`.  Here's the missing comma.