Make all-gdbsupport depend on all-bfd

Make all-gdbsupport depend on all-bfd

Trying to run "make all-gdbsupport" at the top-level in a build from scratch
results in:

make[2]: Entering directory '/home/smarchi/build/binutils-gdb/gdbsupport'
  CC       agent.o
In file included from /home/smarchi/src/binutils-gdb/gdbsupport/common-defs.h:133,
                 from /home/smarchi/src/binutils-gdb/gdbsupport/agent.c:20:
/home/smarchi/src/binutils-gdb/gdbsupport/common-types.h:35:10: fatal error: bfd.h: No such file or directory
   35 | #include "bfd.h"
      |          ^~~~~~~

Before building all-gdbsupport, we need all-bfd to run, so that bfd.h is
generated.

(Once this patch is merged in the binutils-gdb repo, I'll send it to gcc
to keep the files in sync.)

ChangeLog:

	* Makefile.def: Add dependencies of all-gdbsupport on all-bfd.
	* Makefile.in: Re-generate.