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

On Linux. Required installs are the gcc-built Qt libraries themselves,
the "Sources" and "Qt Debug Information Files" components.

Fixes: QTCREATORBUG-20693
Change-Id: I920efd641ce3ee4583741ea1db0bea18031adc51
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

share/qtcreator/debugger/gdbbridge.py

@@ -994,8 +994,21 @@ class Dumper(DumperBase):
             qtCoreMatch = re.match('.*/libQt5?Core[^/.]*\.so', name)
 
         if qtCoreMatch is not None:
+            self.addDebugLibs(objfile)
             self.handleQtCoreLoaded(objfile)
 
+    def addDebugLibs(self, objfile):
+        # The directory where separate debug symbols are searched for
+        # is "/usr/lib/debug".
+        try:
+            cooked = gdb.execute('show debug-file-directory', to_string=True)
+            clean = cooked.split('"')[1]
+            newdir = '/'.join(objfile.filename.split('/')[:-1])
+            gdb.execute('set debug-file-directory %s:%s' % (clean, newdir))
+        except:
+            pass
+
+
     def handleQtCoreLoaded(self, objfile):
         fd, tmppath = tempfile.mkstemp()
         os.close(fd)

src/plugins/debugger/debuggersourcepathmappingwidget.cpp

@@ -62,7 +62,7 @@ QStringList qtBuildPaths()
                 "c:/users/qt/work/qt",
                 "c:/Users/qt/work/install"};
     } else {
-        return {};
+        return { "/home/qt/work/qt" };
     }
 }
 
@@ -450,7 +450,7 @@ DebuggerSourcePathMappingWidget::SourcePathMap
     SourcePathMap rc = in;
     for (const QString &buildPath : qtBuildPaths()) {
         if (!rc.contains(buildPath)) // Do not overwrite user settings.
-            rc.insert(buildPath, qtInstallPath);
+            rc.insert(buildPath, qtInstallPath + "/../Src");
     }
     return rc;
 }