gdb/compile: add missing entry in bfd_link_callbacks array

gdb/compile: add missing entry in bfd_link_callbacks array

clang 19 fails to build gdb with this error:

    /home/simark/src/binutils-gdb/gdb/compile/compile-object-load.c:302:3: error: cannot initialize a member subobject of type 'void (*)(const char *, ...) __attribute__((noreturn))' with an lvalue of type 'void (const char *, ...)'
      302 |   link_callbacks_einfo, /* einfo */
          |   ^~~~~~~~~~~~~~~~~~~~

This illustrates that the bfd_link_callbacks array is missing an entry
for the "fatal" callback, add it.

The fatal field was added very recently, in d26161914 ("PR 32603, more
ld -w misbehaviour").  We're lucky that the new callback was marked with
the noreturn attribute and that clang checks that, otherwise this would
have gone unnoticed.

Change-Id: I68b63d89f2707359e6254da23bdc0776b0e03ba2