I see the following error when compiling ruby from scratch using rbenv:

In file included from debug.c:27:
./vm_callinfo.h:183:9: error: use of undeclared identifier 'RUBY_FUNCTION_NAME_STRING'
        rp(ci);
        ^
./internal.h:89:72: note: expanded from macro 'rp'
#define rp(obj) rb_obj_info_dump_loc((VALUE)(obj), __FILE__, __LINE__, RUBY_FUNCTION_NAME_STRING)

I updated rbenv and rbenv-build to latest, to no avail.

According to stack overflow, the solution, that worked for me, was to update xcode:

sudo rm -rf /Library/Developer/CommandLineTools
sudo xcode-select --install

.^.