oss-fuzz: added no-fuzz target / updated build command to match actual flags

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Having an executable without the fuzzing makes it easier to debug things. I had several issues reproducing crashes with the production binary so this should help to figure out what is different.

This will also allow us to profile the binary used for fuzzing and make it more performant. We can even use the FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION define (which is specified by OSS-Fuzz) to disable parts of the code which might impact that.

The Makefile actually has many shortcomings. -j does not work because we specify all files in one command and we also do not use the matchcompiler. Since no object files are being stored it will also always compile the whole source which makes things very tedious if you are using it locally. We should probably have a Makefile based on the actual one also generate by dmake. I have a prototype of that locally but it is not ready yet.