RFC: bfd_section should not be NULL in call to prim_record_minimal_*

[Joel Brobecker <brobecker@adacore.com>]

Hello,

It seems that creating breakpoints no longer works on ppc-aix:

    % gdb foo
    (gdb) b main
    /[...]/progspace.c:216: internal-error: set_current_program_space: Assertion `pspace != NULL' failed.
    A problem internal to GDB has been detected,
    further debugging may prove unreliable.
    Quit this debugging session? (y or n)

Patch #2 explains what is going on, but basically, xcoffread.c
creates minimal symbols where the obj_section is not set. At first
sight, minsyms.h seems to indicate that it is OK, if you look at
prim_record_minimal_symbol_full's documentation:

   BFD_SECTION - the symbol's BFD section; used to find the
   appropriate obj_section for the minimal symbol.  This can be NULL.
                                                    ^^^^^^^^^^^^^^^^

But I think it is wrong, because I think a lot of places in the GDB code
make the assumption that a minimal symbol's obj_section is not NULL, and
the only way to set it, I think, is to have the BFD section.

So, I think the function documentation should be changed to remove
the permission to pass NULL, and a gdb_assert should also be added
to verify that SYMBOL_OBJ_SECTION (msymbol) != NULL after the
BFD section to obj_section search.

In the meantime, patch #2 fixes the problem by making sure that we
always pass a BFD section.  I haven't tested it against the official
testsuite, I will do so now, but I also wanted to start this discussion
before I forget.