gdb: more current_program_space->core_bfd() removal

This commit changes the signature of the gdbarch_core_info_proc method
so that it takes a 'struct bfd *' as an extra argument.  This argument
is used to pass through the core file bfd pointer.

Now, in corelow.c, when calling gdbarch_core_info_proc, we can pass
through current_program_space->core_bfd() as the argument.  Within the
implementations, (Linux and FreeBSD) we can use this argument rather
than having to access the core file through current_program_space.

This reduces the use of global state, which I think is a good thing.

There should be no user visible changes after this commit.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

gdb/gdbarch_components.py

@@ -2554,11 +2554,15 @@ Method(
     comment="""
 Implement the "info proc" command for core files.  Note that there
 are two "info_proc"-like methods on gdbarch -- one for core files,
-one for live targets.
+one for live targets.  CBFD is the core file being read from.
 """,
     type="void",
     name="core_info_proc",
-    params=[("const char *", "args"), ("enum info_proc_what", "what")],
+    params=[
+        ("struct bfd *", "cbfd"),
+        ("const char *", "args"),
+        ("enum info_proc_what", "what")
+    ],
     predicate=True,
 )