debuginfo-gdb tests can't handle new gdb that supports rust

[infinity0]

Lots of error: line not found in debugger output e.g. see buildlog for 1.13.0~~nightly.20160904, shorter snippet of one failure: https://paste.debian.net/812883/

test result: FAILED. 37 passed; 65 failed; 3 ignored; 0 measured

[michaelwoerister]

@brson @alexcrichton We need test infrastructure that uses a Rust-enabled version of GDB.

cc @tromey @Manishearth

[Manishearth]

set language rust might be necessary in those tests?

[alexcrichton]

Discussed during tools triage today, conclusions were:

• Ideally tests would support all versions of GDB, perhaps even including a gdb/lldb style split of assertions and commands for newer versions of GDB
• We should have bots testing both versions of GDB
  • This may involve two bots with two versions of GDB
  • It may also involve one bot testing two versions of GDB

[nagisa]

This is an example of a failure, which also makes it quite obvious why the tests fail:

error: line not found in debugger output: $4 = {a = 3, b = 4, c = 5, d = 6, e = 7, f = 8, g = 9, h = 10}
<snip>
$4 = function_arg_initialization::BigStruct {a: 3, b: 4, c: 5, d: 6, e: 7, f: 8, g: 9, h: 10}

This is a very nasty failure case because I haven’t seen a successful run of tests on arch for months now.

[TimNN]

I've got a PR ready, which fixes all those tests (for GDB trunk), #37410.