System Workbench for STM32

In case anyone else is having the same problem:
Help -> Installation Details -> Installation History -> Delete
does not actually delete the files. Also, install doesn't actually re-install by expanding the archive. So no amount of Delete/Revert/Install made any difference.

In my case, it appears somehow I ended up with an incompletely-unzipped directory at:

C:\OpenSTM32\SystemWorkbench\plugins\fr.ac6.mcu.externaltools.arm-none.win32_1.16.0.201807130628/tools/compiler

I could not figure out how to delete the folder or otherwise convince Eclipse to re-install it. I ended up manually unzipping the file:

st-gnu-arm-gcc-7-2017-q4-major_gdb-5_4-2016q3-win32.zip

Now, the GNU ARM toolchain is complete again.