Replace /O2 with /O1 compiler flag on Windows
Replace /O2 with /O1 compiler flag on Windows

After the update to Visual Studio v16.4.0, the /O2 optimization flag in the interpreter make many (25%) of the tests failing.
Try to re-enable /O2 after the upgrade of llvm & clang, or after updating Visual Studio (v16.5.0 beta 2 still doesn't work)

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