Make sure our linker gets used when compiling Tor Browser for Windows
#12753 (moved) zeroed out the timestamp in the PE header but surprisingly not everywhere (e.g. not in the tor.exe). This might be due to the fact that our own linker is not used in these cases. See the hint in gitian-firefoy.yml
XXX: the path to ld is hardcoded in mingw..
which would explain why tor.exe and the mingw-w64 libs we build in gitian-utils.yml are affected.