[Bug other/60470] Building gcc using "make" fails after a successful configure when flex and bison are not installed.

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60470

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
It's also documented: http://gcc.gnu.org/install/prerequisites.html#TOC1

While it would be nice if it failed earlier, we don't want configure to fail
for releases if flex isn't installed, because it isn't needed for releases, so
it would be non-trivial to change this.

If you're building a snapshot or building from the source repo then you are
expected to be capable of installing an extra package or two.