Get a working content process sandbox for Tor Browser on Windows

We are about to compile Tor Browser for Windows with --disable-sandbox as it breaks with mingw-w64 otherwise (https://bugzilla.mozilla.org/show_bug.cgi?id=1042426). One of the main problems is that SEH is not available in GCC mainly due to patent issues (See: https://gcc.gnu.org/wiki/WindowsGCCImprovements section Structured Exception Handling (SEH)). According to Jacek the patent expired but still there has no one written the proper code for GCC yet.

We might want to think about ways to get that fixed for us by third parties I guess.