Understand impact of fixing the build for the antlr FASM modules

Before
```
03:04:13 | cd /root/work/xc7/counter_test/build/zybo && symbiflow_write_bitstream -d zynq7 -f top.fasm -p xc7z010clg400-1 -b top.bit
03:04:13 | Writing bitstream ...
03:04:15 | /root/opt/symbiflow/xc7/conda/envs/xc7/lib/python3.7/site-packages/fasm/parser/__init__.py:33: RuntimeWarning: Unable to import fast Antlr4 parser implementation.
03:04:15 | ImportError: cannot import name 'antlr_to_tuple' from 'fasm.parser' (/root/opt/symbiflow/xc7/conda/envs/xc7/lib/python3.7/site-packages/fasm/parser/__init__.py)
03:04:15 |
03:04:15 | Falling back to the much slower pure Python textX based parser
03:04:15 | implementation.
03:04:15 |
03:04:15 | Getting the faster antlr parser can normally be done by installing the
03:04:15 | required dependencies and then reinstalling the fasm package with:
03:04:15 | pip uninstall
03:04:15 | pip install -v fasm
03:04:15 |
03:04:15 | """.format(e), RuntimeWarning)
03:04:15 | make: Leaving directory '/root/work/xc7/counter_test'
```

After
```
09:03:53 | cd /root/work/xc7/counter_test/build/zybo && symbiflow_write_bitstream -d zynq7 -f top.fasm -p xc7z010clg400-1 -b top.bit
09:03:53 | Writing bitstream ...
09:03:54 | make: Leaving directory '/root/work/xc7/counter_test'
```