Codemodelbackend: Fix location of binary in build dir and install it

Change-Id: I943e13b92bdaa2ee1e6ead81788da45b40926f60
Reviewed-by: Marco Bubke <marco.bubke@theqtcompany.com>

src/plugins/clangcodemodel/codemodelbackendipcintegration.cpp

@@ -78,7 +78,7 @@ namespace {
 
 QString backendProcessPath()
 {
-    return QCoreApplication::applicationDirPath()
+    return Core::ICore::libexecPath()
             + QStringLiteral("/codemodelbackend")
             + QStringLiteral(QTC_HOST_EXE_SUFFIX);
 }