d/patches: Add fix-filesystem-references.patch

Rylie Pavlikrequested to merge
rpavlik/gcc-mingw-w64:patch-buster into buster

I hit a linking error when using Buster's mingw, and found that it was referenced, along with a patch to solve it, here: https://patches-gcc.linaro.org/patch/12753/#22525

I've simply added the patch from that page (I couldn't find the commit itself on GitHub despite having the hash) and adjusted the paths within it so that buildpackage can at least get started (I haven't run it to completion yet)

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