Use offsetof from the compiler instead of own implementation
Use offsetof from the compiler instead of own implementation

Silences clang -fsanitize=undefined.
Not sure why clang complains here.

MatzeB/libfirm,MatzeB/libfirm,libfirm/libfirm,jonashaag/libfirm,jonashaag/libfirm,killbug2004/libfirm,libfirm/libfirm,8l/libfirm,8l/libfirm,MatzeB/libfirm,killbug2004/libfirm,jonashaag/libfirm,jonashaag/libfirm,davidgiven/libfirm,libfirm/libfirm,killbug2004/libfirm,davidgiven/libfirm,jonashaag/libfirm,MatzeB/libfirm,8l/libfirm,davidgiven/libfirm,killbug2004/libfirm,jonashaag/libfirm,killbug2004/libfirm,MatzeB/libfirm,8l/libfirm,davidgiven/libfirm,libfirm/libfirm,davidgiven/libfirm,8l/libfirm,killbug2004/libfirm,8l/libfirm,jonashaag/libfirm,8l/libfirm,libfirm/libfirm,davidgiven/libfirm,MatzeB/libfirm,davidgiven/libfirm,MatzeB/libfirm,killbug2004/libfirm