I tried using a custom specs file with your Win64 build (I suspect it is the same with other builds) as explained here: I placed it at <mingw64 dir>\lib\gcc\<build>\<version>\specs, but it wasn't working. I used Process Monitor to see if the file was even being read, and found that it is searching in "C:\home\ruben\mingw-w64\toolchain\mingw64mingw64\mingw64\lib\gcc\x86_64-w64-mingw32\specs", which is obviously wrong.
Can you please fix this?
Thank you.

˙uʍop-ǝpısdn sı ɹoʇıuoɯ ɹnoʎ 'sıɥʇ pɐǝɹ uɐɔ noʎ ɟı