Description of problem: Building from the current 1.4.18 .src RPM dies with this error:

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."
   ^~~~~

The problem is in lib/freadahead.c, line 28:

#if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */

This has been a bullet-in-the-chamber since Ulric Drepper nailed the value of __GNU_LIBRARY__ to 6 - in October 1996.

The issue with the left half arises from this upstream glibc commit, as far as I can tell (or possibly a related commit)

https://sourceware.org/git/?p=glibc.git;a=commit;f=libio/libio.h;h=48a8f8328122ab8d06b7333cb87be46feeaf7cca

which is intended to dissuade people from poking around in the internals.  Simply raising the compare to == 6 doesn't help, as then it goes:

freadahead.c:32:26: error: '_IO_IN_BACKUP' undeclared (first use in this function

So more surgery is needed...
2.27.9000015.fc29 breaks
2.27.9000-14.fc29 was OK


Version-Release number of selected component (if applicable):
m4-1.4.18-6.fc28

How reproducible:
'rpmbuild -bb' against m4-1.4.18-6.fc28.src.rpm on a box that has glibc-2.27.9000-15.fc29.x86_64 installed.

Steps to Reproduce:
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Expected results:


Additional info: