[Bug other/84715] "./configure --disable-multilib && make" fails due to "g++: error: gengtype-lex.c: No such file or directory"

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84715

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
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.