Rust Linux test gdb failure

---- [debuginfo-both] debuginfo/empty-string.rs stdout ----                                                                                                                                                                    [4/1820]
NOTE: compiletest thinks it is using GDB with native rust support
NOTE: compiletest thinks it is using GDB version 7012000                     
                                                                  
error: line not found in debugger output: $2 = ""                         
status: exit code: 0            
command: "/usr/bin/gdb" "-quiet" "-batch" "-nx" "-command=/build/rust/build/x86_64-unknown-linux-gnu/test/debuginfo/empty-string/empty-string.debugger.script"
stdout:                                             
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GNU gdb (Debian 7.12-6) 7.12.0.20161007-git
Copyright (C) 2016 Free Software Foundation, Inc.               
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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and "show warranty" for details.                                                     
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.                      
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Breakpoint 1 at 0x139f: file /build/rust/src/test/debuginfo/empty-string.rs, line 32.
[Thread debugging using libthread_db enabled]    
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
                                                           
Breakpoint 1, empty_string::main::h2741c6f3b053ffe9 () at /build/rust/src/test/debuginfo/empty-string.rs:32
32          zzz(); // #break              
$1 = ""
$2 = &str {data_ptr: 0x5555555554c3 <__rustc_debug_gdb_scripts_section__> "\001gdb_load_rust_pretty_printers.py\000", length: 0}
A debugging session is active.
                                          
        Inferior 1 [process 1528] will be killed.
                                                                                       
Quit anyway? (y or n) [answered Y; input not from terminal]                   

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stderr:  
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thread 'main' panicked at 'explicit panic', src/tools/compiletest/src/runtest.rs:3425:9
note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.


failures:
    [debuginfo-both] debuginfo/empty-string.rs

test result: FAILED. 73 passed; 1 failed; 47 ignored; 0 measured; 0 filtered out

thread 'main' panicked at 'Some tests failed', src/tools/compiletest/src/main.rs:516:22