build error with glibc > 2.28 in m4-1.4.18/lib/freadahead.c

Hello,

in order to build sedutil (https://github.com/ChubbyAnt/sedutil) on 
Fedora 30 I encountered a build error in m4-1.4.18.


Error Message:

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."
    92 |  #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."
       |   ^~~~~
   CC       mbrtowc.o
make[5]: *** [Makefile:1915: freadahead.o] Error 1
make[5]: *** Waiting for unfinished jobs....
fseeko.c: In function 'rpl_fseeko':
fseeko.c:110:4: error: #error "Please port gnulib fseeko.c to your 
platform! Look at the code in fseeko.c, then report this to bug-gnulib."
   110 |   #error "Please port gnulib fseeko.c to your platform! Look at 
the code in fseeko.c, then report this to bug-gnulib."
       |    ^~~~~
make[5]: *** [Makefile:1915: fseeko.o] Error 1
make[4]: *** [Makefile:1674: all] Error 2
make[3]: *** [Makefile:1572: all-recursive] Error 1
make[2]: *** [Makefile:1528: all] Error 2
make[1]: *** [package/pkg-generic.mk:230: 
/home/relentless/Playground/sedutil/images/scratch/buildroot/64bit/build/host-m4-1.4.18/.stamp_built] 
Error 2
make: *** [Makefile:79: _all] Error 2


This error occurs because I have glibc-2.29 installed on my Fedora 30 
system instead of glibc-2.27 on e.g. Ubuntu 18.04 LTS.

Apparently this is a known issue introduced by a change in glibc-2.28. I 
guess it can be patched similar to these two commits in gnulib.

https://github.com/coreutils/gnulib/commit/4af4a4a71827c0bc5e0ec67af23edef4f15cee8e#diff-5bcce8ce55246264586c4aed2a45ff89

https://github.com/coreutils/gnulib/commit/74d9d6a293d7462dea8f83e7fc5ac792e956a0ad#diff-5bcce8ce55246264586c4aed2a45ff89


Although I am very new two building from source, I hope I can could help.

Best regards,
Marius