Running `./configure --disable-multilib && make` fails due to ``` g++: error: gengtype-lex.c: No such file or directory g++: fatal error: no input files compilation terminated. make[3]: *** [build/gengtype-lex.o] Error 1 make[3]: *** Waiting for unfinished jobs.... Makefile:2666: recipe for target 'build/gengtype-lex.o' failed ``` on a pretty empty docker image. I recreated the issue on Ubuntu 14.04, 16.04, 17.10 and 18.04 preview as well as Debian oldstable, stable and testing inside GitLab CI, see https://gitlab.com/krichter/gcc/pipelines/18408388 for details and [.gitlab-ci.yml](https://gitlab.com/krichter/gcc/blob/gitlab-ci/.gitlab-ci.yml) for the build instructions. In case this is a user error, it'd be nice if `configure` would check that all conditions for the configured build are fulfilled and otherwise fail with a helpful error message. experienced with 4225b5dcdbcadaa3d7605582f735d02b6fc50cdf
Don't run ./configure in the source dir: https://gcc.gnu.org/wiki/FAQ#configure If you're building a snapshot or modifying the source, you need Flex: https://gcc.gnu.org/install/prerequisites.html#Tools_002fpackages-necessary-for-modifying-GCC We don't want the configure script to require flex, because most users don't need it. If you're building a snapshot (not an official release) or modifying the source then you're expected to read the docs and install the required prerequisites.
As documented.