fixup reportgenerator invocations on non-windows machines

[baronfel]

Proposed Changes

I had to make some changes to the process-spawning code for reportgenerator on a project I had in order to get it to run.

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

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• Build and tests pass locally
• I have added tests that prove my fix is effective or that my feature works (if appropriate)
• I have added necessary documentation (if appropriate)

Further comments

The two main fixes are

1. mono prefix when on non-windows, and
2. need to wrap the prefix argument in quotes so that shells don't try to expand them.