flex 2.6.4 can't be built for riscv64 arch

[dmitryikh]

The latest release flex 2.6.4 is dated to 2017 and contains old configure scripts, which can't recognize new cpu arch:

Build log (issued by conan2 package manger):

flex/2.6.4: RUN: "/root/.conan2/p/b/flex4f66148738957/b/configure" --disable-shared --enable-static --prefix=/ '--bindir=${prefix}/bin' '--sbindir=${prefix}/bin' '--libdir=${prefix}/lib' '--includedir=${prefix}/include' '--oldincludedir=${prefix}/include' --disable-nls --disable-bootstrap HELP2MAN=/bin/true M4=m4 ac_cv_func_malloc_0_nonnull=yes ac_cv_func_realloc_0_nonnull=yes ac_cv_func_reallocarray=no 
checking build system type... build-aux/config.guess: unable to guess system type

This script, last modified 2015-08-20, has failed to recognize
the operating system you are using. It is advised that you
download the most up to date version of the config scripts from

  http://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.guess;hb=HEAD
and
  http://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.sub;hb=HEAD

If the version you run (build-aux/config.guess) is already up to date, please
send the following data and any information you think might be
pertinent to <config-patches@gnu.org> in order to provide the needed
information to handle your system.

config.guess timestamp = 2015-08-20

uname -m = riscv64
uname -r = 6.10.14-linuxkit
uname -s = Linux
uname -v = #1 SMP Thu Aug 14 19:26:13 UTC 2025

/usr/bin/uname -p = riscv64
/bin/uname -X     = 

hostinfo               = 
/bin/universe          = 
/usr/bin/arch -k       = 
/bin/arch              = riscv64
/usr/bin/oslevel       = 
/usr/convex/getsysinfo = 

UNAME_MACHINE = riscv64
UNAME_RELEASE = 6.10.14-linuxkit
UNAME_SYSTEM  = Linux
UNAME_VERSION = #1 SMP Thu Aug 14 19:26:13 UTC 2025
configure: error: cannot guess build type; you must specify one

flex/2.6.4: ERROR: 
Package 'fa2a3ec2ecd1e20067aa2d35355a3886c2ace26e' build failed
flex/2.6.4: WARN: Build folder /root/.conan2/p/b/flex4f66148738957/b
ERROR: flex/2.6.4: Error in build() method, line 76
	autotools.configure()
	ConanException: Error 1 while executing

If I apply the proposed solutions ( downloading fresh config.guess and config.sub), everything works fine.

Can we have a new release for flex with updated autotools?

[GitMensch]

I think downporting is out of scope - distro packagers are good in that.
For the next release... the only point was to have it automated #480, but I agree that updating those files from gnulib https://cgit.git.savannah.gnu.org/cgit/gnulib.git/tree/build-aux is totally reasonable (config.git may have "a bit more unstable" versions, so I suggest to go with gnulib).

@dmitryikh Would you mind doing that and sending a PR? I don't think executing autogen.sh afterwards will change any files, will it?
.... but kind of related - build tools - is also #574. Doing that (which possibly changes more) before a release would be good.