Build error on macOS (`SSIZE_MAX` undefined)

[eschnett]

I am building OpenMPI 5.0.0 on macOS with a MacPorts-installed GCC 13.2.

My configure options are

$ ./configure --prefix=$HOME/openmpi-5.0.0 --with-libevent=internal CC=gcc CXX=g++ FC=gfortran

This fails with the error message

get_elements_x.c: In function 'PMPI_Get_elements_x':
get_elements_x.c:77:63: error: 'SSIZE_MAX' undeclared (first use in this function); did you mean 'RSIZE_MAX'?
   77 |         if (OMPI_SUCCESS == ret && internal_count <= (size_t) SSIZE_MAX) {
      |                                                               ^~~~~~~~~
      |                                                               RSIZE_MAX
get_elements_x.c:77:63: note: each undeclared identifier is reported only once for each function it appears in

Adding the lines

#ifndef SSIZE_MAX
#define SSIZE_MAX LONG_MAX
#endif

after the #include <limits.h> resolves the issue for me.

I'm sure there is a more elegant way, probably requiring a certain POSIX level, but I could not figure it out.