Debugger: Fix use of external debug info for installer-based Qt

On macOS. This amends ada0e43c93. Fixes the default build directory
on macOS as this is different compared to Linux.
Beside this the patch passes the configured mappings of build dir and
source locations to the lldb.

Task-number: QTCREATORBUG-20693
Change-Id: I4258c09ec96fbdc1a713ae82df6bcab04129570c
Reviewed-by: hjk <hjk@qt.io>

src/plugins/debugger/debuggersourcepathmappingwidget.cpp

@@ -61,6 +61,8 @@ QStringList qtBuildPaths()
                 "C:/work/build/qt5_workdir/w/s",
                 "c:/users/qt/work/qt",
                 "c:/Users/qt/work/install"};
+    } else if (HostOsInfo::isMacHost()) {
+        return { "/Users/qt/work/qt" };
     } else {
         return { "/home/qt/work/qt" };
     }

src/plugins/debugger/lldb/lldbengine.cpp

@@ -35,6 +35,7 @@
 #include <debugger/terminal.h>
 
 #include <debugger/breakhandler.h>
+#include <debugger/debuggersourcepathmappingwidget.h>
 #include <debugger/disassemblerlines.h>
 #include <debugger/moduleshandler.h>
 #include <debugger/registerhandler.h>
@@ -318,6 +319,15 @@ void LldbEngine::runEngine()
     if (rp.startMode == AttachCore)
         cmd.arg("coreFile", rp.coreFile);
     runCommand(cmd);
+
+    const SourcePathMap sourcePathMap =
+        DebuggerSourcePathMappingWidget::mergePlatformQtPath(rp,
+                Internal::globalDebuggerOptions()->sourcePathMap);
+    for (auto it = sourcePathMap.constBegin(), cend = sourcePathMap.constEnd();
+         it != cend;
+         ++it) {
+        executeDebuggerCommand("settings append target.source-map " + it.key() + ' ' + it.value());
+    }
 }
 
 void LldbEngine::interruptInferior()