gdb, linespec: avoid multiple locations with same PC

gdb, linespec: avoid multiple locations with same PC

Setting a BP on a line like this would incorrectly yield two BP locations:

01 void two () { {int var = 0;} }

(gdb) break 1
Breakpoint 1 at 0x1164: main.cpp:1. (2 locations)

(gdb) info breakpoints
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   <MULTIPLE>
1.1                         y   0x0000000000001164 in two() at main.cpp:1
1.2                         y   0x0000000000001164 in two() at main.cpp:1

In this case decode_digits_ordinary () returns two SALs, exactly matching the
requested line.  One for the entry PC and one for the prologue end PC.  This
was
tested with GCC, CLANG and ICPX.  Subsequent code tries to skip the prologue
on these PCs, which in turn makes them the same.

To fix this, ignore SALs with the same PC and program space when adding to the
list of SALs.

This will then properly set only one location:

(gdb) break 1
Breakpoint 1 at 0x1164: file main.cpp, line 1

(gdb) info breakpoints
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x0000000000001164 in two() at main.cpp:1

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