gdb: lookup minsym using section in find_sal_for_pc_sect

gdb: lookup minsym using section in find_sal_for_pc_sect

The find_sal_for_pc_sect function attempts to find the line that is
closest to a pc+section in the available symbols. One of the first thing
the function does is search for a bound minimal symbol corresponding to
that pc. In its original version, the lookup is performed by
lookup_minimal_symbol_by_pc, discarding the section. This is misleading
and may cause issues with overlay debugging if a second minsym with the
same pc (but a different section) can be found -- although this is only
in theory after inspecting the code, as I have no way to test this on a
system supporting overlays.

This should have no observable effects for the end user. One slight
benefit is that we can avoid a section lookup inside
lookup_minimal_symbol_by_pc_section if the caller does provide a
section.

Since the section is already passed as an argument to the function, the
proposed change forwards this section to the minsym lookup section.

Approved-By: Tom Tromey <tom@tromey.com>
Change-Id: I86a16bf397ea7167d3e9c7db79b8d7901fad1a97