Backtrace DLLs fail to build on Win10/MSYS2

"make ebacktrace" fails on current Win10/MSYS2.

It used to build up to the last GCC release from the MinGW-w64 project (8.1.0): https://sourceforge.net/projects/mingw-w64/files/Toolchains%20targetting%20Win64/Personal%20Builds/mingw-builds/8.1.0/threads-posix/seh

While I could fix compiling with the GCC 9.x that comes with MSYS2, the resulting DLL doesn't actually work:

Fix (64bit): > pacman -S mingw-w64-x86_64-expat mingw-w64-x86_64-gettext

Working command line (64bit): > gcc -O2 -std=gnu99 -ggdb -shared -Wall -Wextra -static-libgcc -o ebacktrace1-64.dll platform/Windows/src/backtrace.c -I/mingw64/include/binutils/ -L/mingw64/lib/binutils/ -lbfd -liberty -limagehlp -lintl