[OSX] lldb cannot read bitfield dwarf debug info generated by -mmacosx-version-min=10.11

Type: Debugger

Describe the bug

• OS and Version: MacOSX 10.4.1
• VS Code Version: 1.29.0
• C/C++ Extension Version: 0.20.1
• A clear and concise description of what the bug is.

Starting from MacOSX target 10.11, clang tunes it's debug information for lldb. This causes the version of lldb embedded in the cpptools extension to misreport bitfield values.

To Reproduce

#include <stdio.h>

int main() {
    struct Test {
        unsigned short a;
        unsigned short b : 1;
        unsigned short c: 15;
    };

    Test x = {0};
    x.a = 5;
    printf("%hu", x.b);
    return 0;
}

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "(lldb) Launch",
            "type": "cppdbg",
            "request": "launch",
            "program": "${workspaceFolder}/a.out",
            "args": [],
            "stopAtEntry": false,
            "cwd": "${workspaceFolder}",
            "environment": [],
            "externalConsole": true,
            "MIMode": "lldb"
        }
    ]
}

Steps to reproduce the behavior:

1. Run clang++ test.cc -mmacosx-version-min=10.11 -g
2. Place a breakpoint at line 10: x.a = 5
3. Launch debugger
4. Step over x.a = 5 and see that x.b or x.c changes value (lldb cannot find the right addresses for the bitfields.

Additional context
Compilation where older lldb works:

1. clang++ -c test.cc -mmacosx-version-min=10.10 -g
2. clang++ -c test.cc -mmacosx-version-min=10.11 -ggdb

Inizia riproducendo il caso minimo test.cc con clang++ usando -mmacosx-version-min=10.10 e 10.11, quindi avvialo con la configurazione .vscode/launch.json fornita. Confronta come il debugger segnala x.b e x.c dopo aver eseguito un'operazione step over su x.a = 5; completato significa che i valori dei bitfield rimangono corretti per il target 10.11.