[patch] Fixes problem setting breakpoint in dynamic loader

[PAUL GILLIAM]

On PowerPC-64, with 64-bit executables, GDB has been giving this message
for a while:

        warning: Unable to find dynamic linker breakpoint function.
        GDB will be unable to debug shared library initializers
        and track explicitly loaded dynamic code.

This is because "enable_break()" in solib-svr4.c was looking for the
symbol "._dl_debug_state" in the 64-bit dynamic loader and not finding
it.  This should not be a surprise because these 'dot' symbols have not
been used for a while.

The reason that the non-'dot' symbol was also passed by, is that it
points into a data section and the existing code only checked code
sections.

If none of the symbols on the list was found in a code section, the
attached patch looks in data sections.  When it finds one, and the data
section is either '.plt' or '.opd', then the address points to a
function descriptor which is then used to find the corresponding code
address where the breakpoint can be set.

OK to commit?

-=# Paul #=-
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