Moc: don't make variables inside an unnamed namespace static

Because an unnamed namespace, and variables inside it, have internal
linkage[1]; and the variable is constexpr in this case so static
redundant.

This fixes a clang-tidy warning:
readability-static-definition-in-anonymous-namespace

[1] https://eel.is/c++draft/basic.link#4

Change-Id: I95600214cd51b03872ee22995d93d1b5658d5a18
Fixes: QTBUG-112870
Pick-to: 6.5
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit 5a523981f46550034bb354075ff36444a860109f)
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>

src/tools/moc/generator.cpp

@@ -276,7 +276,7 @@ void Generator::generateCode()
 
     fprintf(out, "\n#ifdef QT_MOC_HAS_STRINGDATA\n"
                  "struct qt_meta_stringdata_%s_t {};\n"
-                 "static constexpr auto qt_meta_stringdata_%s = QtMocHelpers::stringData(",
+                 "constexpr auto qt_meta_stringdata_%s = QtMocHelpers::stringData(",
             qualifiedClassNameIdentifier.constData(), qualifiedClassNameIdentifier.constData());
     {
         char comma = 0;