vtable symbols are not marked artificial in DWARF

I tried this code, from the gdb testsuite:

fn empty () {
}

fn main () {
    let array = [1,2,3,4];
    let slice = &array[1..2];
    let hello = "hello";

    empty();			// STOP
}

I compiled with -g.

Examining the resulting DWARF, I see:

 <1><2a>: Abbrev Number: 2 (DW_TAG_variable)
    <2b>   DW_AT_name        : (indirect string, offset: 0xf3): <std::rt::lang_start::{closure_env#0}<()> as core::ops::function::Fn<()>>::{vtable}
    <2f>   DW_AT_type        : <0x3d>
    <33>   DW_AT_location    : 9 byte block: 3 80 24 5 0 0 0 0 0 	(DW_OP_addr: 52480)

I think this should be marked with DW_AT_artificial, as it does not correspond to any user-written code in the CU. This will let gdb filter out these variables when displaying globals from a CU.

Start by reproducing the issue with the Rust snippet and -g, then inspect the emitted DWARF entry for the vtable variable and compare it with the gdb testsuite's expectations. Done means compiler-generated vtable symbols are marked with DW_AT_artificial so gdb can filter them from user-visible globals.