https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91879
--- Comment #10 from Stas Sergeev <stsp at users dot sourceforge.net> --- (In reply to Jonathan Wakely from comment #9) > It's possible the paths passed to -isystem should be prefixed with = when a > sysroot is in use, Great idea! Maybe it can even be unconditional, as w/o --sysroot it won't change anything? I hacked that solution in. Also I've found that I was setting --with-build-sysroot wrongly in the previous example: I included prefix into it, but it shouldn't be there. Now with your = idea I've got further only for a tiny bit. It fails on the same conftest as before. It now finds the headers! But fails to find libs... --- configure:4135: /home/stas/src/build-gcc/build/djcross-gcc-9.2.0/djcross/./gcc/x gcc -B/home/stas/src/build-gcc/build/djcross-gcc-9.2.0/djcross/./gcc/ -B/usr/loc al/cross/i586-pc-msdosdjgpp/bin/ -B/usr/local/cross/i586-pc-msdosdjgpp/lib/ -isy stem=/usr/local/cross/i586-pc-msdosdjgpp/include -isystem=/usr/local/cross/i586- pc-msdosdjgpp/sys-include --sysroot=/home/stas/src/build-gcc/ttt -o conftest - g -O2 conftest.c >&5 /home/stas/src/build-gcc/ttt/usr/local/cross/bin/i586-pc-msdosdjgpp-ld: cannot f ind crt0.o: No such file or directory /home/stas/src/build-gcc/ttt/usr/local/cross/bin/i586-pc-msdosdjgpp-ld: cannot f ind -lc collect2: error: ld returned 1 exit status --- If I correct -B options above, then it links! Any firther ideas? :) We are really getting close to the solution. > but prefixing them with $DESTDIR is definitely wrong. I renamed the ticket. Sorry for misleading conclusions.