https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82708
--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- If you have correctly configured GCC so that it can find the system headers at configure time, include-fixed/limits.h should be constructed as a concatentation of limitx.h, glimits.h and limity.h and thus include libc's limits.h indirectly. If $(LIMITS_H_TEST) failed to find the system headers, that's what you should be debugging.
