debuginfo: Make sure that only one LLDB test task is run at a time.

Some older versions of LLDB have problems with multiple instances running in parallel. This commit makes sure we don't do that.

src/compiletest/compiletest.rs

@@ -30,7 +30,7 @@ use std::io::fs;
 use std::from_str::FromStr;
 use getopts::{optopt, optflag, reqopt};
 use common::Config;
-use common::{Pretty, DebugInfoGdb, Codegen};
+use common::{Pretty, DebugInfoGdb, DebugInfoLldb, Codegen};
 use util::logv;
 use regex::Regex;
 
@@ -241,6 +241,16 @@ pub fn run_tests(config: &Config) {
         os::setenv("RUST_TEST_TASKS","1");
     }
 
+    match config.mode {
+        DebugInfoLldb => {
+            // Some older versions of LLDB seem to have problems with multiple
+            // instances running in parallel, so only run one test task at a
+            // time.
+            os::setenv("RUST_TEST_TASKS", "1");
+        }
+        _ => { /* proceed */ }
+    }
+
     let opts = test_opts(config);
     let tests = make_tests(config);
     // sadly osx needs some file descriptor limits raised for running tests in