freadseek.c not ported to GNU when building M4

[Mohammad Akhlaghi]

Dear Gnulib,

I am trying to build M4 from source, but it crashes with the following 
Gnulib error after running `make' (which asks to directly contact 
bug-gnulib instead of M4 developers):

  CC       freadseek.lo
freadseek.c: In function 'freadptrinc':
freadseek.c:68:3: error: #error "Please port gnulib freadseek.c to your 
platform! Look at the definition of getc, getc_unlocked on your system, 
then report this to bug-gnulib."
  #error "Please port gnulib freadseek.c to your platform! Look at the 
definition of getc, getc_unlocked on your system, then report this to 
bug-gnulib."
   ^~~~~
make[4]: *** [Makefile:2386: freadseek.lo] Error 1

However, I am doing this build of Arch Linux (using GCC 8.2.1 and glibc 
2.28): a GNU user-space, not a hardly known operating system or 
architecture.

This problem came up on my system after running these commands.

$ git clone git://git.savannah.gnu.org/m4.git
$ cd m4
$ ./bootstrap --copy --gnulib-srcdir=/path/to/gnulib
$ ./configure
$ make

The message asks to look into the definitions of `getc' and 
`getc_unlocked', but when I look into `/usr/include/stdio.h', I only 
have external declarations. If you could point me to the exact place 
where I can find their definitions, I will do it.

Thanks in advance for advice on how to fix this problem,
Cheers,
Mohammad