Compilation of m4 1.4.10 to 1.4.18 fails due to "Please port gnulib freadahead.c to your platform!" on Ubuntu 18.10

The building of tarball releases of GNU m4 1.4.10 to 1.4.18 (didn't test all hotfix versions, but I assume the error is consistent among this range) with ./configure && make -j1 and git git repository http://git.savannah.gnu.org/r/m4.git with ./bootstrap && ./configure && make -j1 (commit cvs-readonly-359-gd69fa528 i.e. HEAD of master) fails due to

freadahead.c: In function 'freadahead':
freadahead.c:92:3: error: #error "Please port gnulib freadahead.c to your platform! Look at the definition of fflush, fread, ungetc on your system, then report this to bug-gnulib."
  #error "Please port gnulib freadahead.c to your platform! Look at the definition of fflush, fread, ungetc on your system, then report this to bug-gnulib."
   ^~~~~
make[3]: *** [Makefile:1910: freadahead.o] Error 1
make[3]: Leaving directory '/mnt/data/sources/m4-1.4.18/lib'

I'm very confused by this error and according to a superficial google search the problem is the consequence of an overly long ignored upstream update, see e.g. https://bugzilla.redhat.com/show_bug.cgi?id=1573342 with the genius documentation of the fix "Thanks for the bug report, fixed!" - if that doesn't help others...

I tried to build glibc from source and install it into a custom prefix[1]. 2.28 and 2.27 exhibit the same issue and 2.26 fails due to

make[2]: Verzeichnis „/mnt/data/sources/glibc-2.26/inet“ wird betreten
gcc ../sysdeps/unix/sysv/linux/if_index.c -c -std=gnu11 -fgnu89-inline  -O2 -Wall -Werror -Wundef -Wwrite-strings -fmerge-all-constants -fno-stack-protector -frounding-math -g -Wstrict-prototypes -Wold-style-definition     -ftls-model=initial-exec   -U_FORTIFY_SOURCE   -I../include -I/mnt/data/sources/glibc-2.26-build/inet  -I/mnt/data/sources/glibc-2.26-build  -I../sysdeps/unix/sysv/linux/x86_64/64  -I../sysdeps/unix/sysv/linux/x86_64  -I../sysdeps/unix/sysv/linux/x86  -I../sysdeps/x86/nptl  -I../sysdeps/unix/sysv/linux/wordsize-64  -I../sysdeps/x86_64/nptl  -I../sysdeps/unix/sysv/linux/include -I../sysdeps/unix/sysv/linux  -I../sysdeps/nptl  -I../sysdeps/pthread  -I../sysdeps/gnu  -I../sysdeps/unix/inet  -I../sysdeps/unix/sysv  -I../sysdeps/unix/x86_64  -I../sysdeps/unix  -I../sysdeps/posix  -I../sysdeps/x86_64/64  -I../sysdeps/x86_64/fpu/multiarch  -I../sysdeps/x86_64/fpu  -I../sysdeps/x86/fpu/include -I../sysdeps/x86/fpu  -I../sysdeps/x86_64/multiarch  -I../sysdeps/x86_64  -I../sysdeps/x86  -I../sysdeps/ieee754/float128  -I../sysdeps/ieee754/ldbl-96/include -I../sysdeps/ieee754/ldbl-96  -I../sysdeps/ieee754/dbl-64/wordsize-64  -I../sysdeps/ieee754/dbl-64  -I../sysdeps/ieee754/flt-32  -I../sysdeps/wordsize-64  -I../sysdeps/ieee754  -I../sysdeps/generic  -I.. -I../libio -I.   -D_LIBC_REENTRANT -include /mnt/data/sources/glibc-2.26-build/libc-modules.h -DMODULE_NAME=libc -include ../include/libc-symbols.h  -DPIC     -DTOP_NAMESPACE=glibc -o /mnt/data/sources/glibc-2.26-build/inet/if_index.o -MD -MP -MF /mnt/data/sources/glibc-2.26-build/inet/if_index.o.dt -MT /mnt/data/sources/glibc-2.26-build/inet/if_index.o
../sysdeps/unix/sysv/linux/if_index.c: In function ‘__if_nametoindex’:
../sysdeps/unix/sysv/linux/if_index.c:46:3: error: ‘strncpy’ specified bound 16 equals destination size [-Werror=stringop-truncation]
   strncpy (ifr.ifr_name, ifname, sizeof (ifr.ifr_name));
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[2]: *** [/mnt/data/sources/glibc-2.26-build/sysd-rules:213: /mnt/data/sources/glibc-2.26-build/inet/if_index.o] Fehler 1
make[2]: Verzeichnis „/mnt/data/sources/glibc-2.26/inet“ wird verlassen
make[1]: *** [Makefile:215: inet/subdir_lib] Fehler 2
make[1]: Verzeichnis „/mnt/data/sources/glibc-2.26“ wird verlassen
make: *** [Makefile:9: all] Fehler 2

and 2.25 due to

strftime_l.c: In function ‘__strftime_internal’:
strftime_l.c:719:4: error: macro expands to multiple statements [-Werror=multistatement-macros]
    digits = d > width ? d : width;          \
    ^~~~~~
strftime_l.c:1260:6: note: in expansion of macro ‘DO_NUMBER’
      DO_NUMBER (1, tp->tm_year + TM_YEAR_BASE);
      ^~~~~~~~~
strftime_l.c:1259:4: note: some parts of macro expansion are not guarded by this ‘else’ clause
    else
    ^~~~
In file included from wcsftime_l.c:23:
strftime_l.c: In function ‘__strftime_internal’:
strftime_l.c:719:4: error: macro expands to multiple statements [-Werror=multistatement-macros]
    digits = d > width ? d : width;          \
    ^~~~~~
strftime_l.c:1260:6: note: in expansion of macro ‘DO_NUMBER’
      DO_NUMBER (1, tp->tm_year + TM_YEAR_BASE);
      ^~~~~~~~~
strftime_l.c:1259:4: note: some parts of macro expansion are not guarded by this ‘else’ clause
    else
    ^~~~
cc1: all warnings being treated as errors
make[2]: *** [../o-iterator.mk:9: /mnt/data/sources/glibc-2.25-build/time/strftime_l.os] Fehler 1

which made me decide to not try out further version.

[The discussion on a report about a similar issue in findutils] suggests to overwrite freadahead.{c,h} from an up-to-date gnulib source root. This causes a chain of problems which is unnecessary to document here as I don't know what I'm doing.

How to get started with fixing, reporting and/or working around this issue?

I'm building m4 from source for a bootstrap script for systems where a user doesn't have privileges to use the package manager. I'm really just interested in building the original GNU m4 from release source tarballs.

An overview of build results on other similarily bare systems is provided at https://gitlab.com/krichter/m4/pipelines/36977411.

[1] In case you're investigating this always install glibc into a custom prefix because an installation in the default prefix /usr/local will most certainly ruine your system. Consider using checkinstall to be sure.