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."
      |   ^~~~~
make[3]: *** [Makefile:1910: freadahead.o] Error 1
make[3]: Leaving directory '/opt/build/m4-1.4.18/lib'
make[2]: *** [Makefile:1674: all] Error 2
make[2]: Leaving directory '/opt/build/m4-1.4.18/lib'
make[1]: *** [Makefile:1572: all-recursive] Error 1
make[1]: Leaving directory '/opt/build/m4-1.4.18'
make: *** [Makefile:1528: all] Error 2