Quote arguments with mingw

Ghost User
2020-10-16T10:57:55+02:00

It turns out that when compiling with MinGW you should also quote arguments to `spawn`. This also revealed two other problems: one where I inadvertently removed the closing `"` from the kernel_library etc. arguments; the other where the arguments to the linker are already quoted and do not need to be quoted again when creating the command line for `CreateProcess`.

Sorry that this all happens in separate MRs, because I first didn't realise the environment on the build server was different, and then wasn't sure how to reproduce it exactly, it was a bit tricky... The platform test runs OK with these changes (https://gitlab.science.ru.nl/clean-and-itasks/clean-platform/-/jobs/109873), so hopefully this is the last change for the time being.