Hi,

I was recently working a bit on debugging support for C# (using Mono)
and I need a way to tell GDB about the lifetime of local variables. In
C#, the JIT engine may decide to store two different variables at the
same stack offset if they aren't used throughout the whole function.

Now I was wondering how to do this - DWARF 2 already has a
`DW_AT_begin_scope' but unfortunately no `DW_AT_end_scope' - can we
add this or something similar as a GNU extension ?

After looking at the code, I found out that `struct symbol' contains a
`ranges' field which seems to do exactly what I want - but this field
isn't used anywhere.

The following patch

* adds a new DWARF 2 attribute DW_AT_end_scope to specify the end of
  a local variable's scope.

* initializes SYMBOL_RANGES() in dwarf2read.c if DW_AT_begin_scope and
  DW_AT_end_scope are specified.

  [FIXME: According to the DWARF 2 specification, this attribute takes
          an offset (DW_FROM_data), not an address - but I found now
          way to get the current frame's address in new_symbol(), this
          needs to be fixed.]

* checks whether the current PC is within the symbol's SYMBOL_RANGES()
  when listing the local variables of a function and when printing a
  variable.