tst_licenses.pl: Fall back to QT_INSTALL_PREFIX/src when looking for qtbase

This makes it possible to check modules that are not checked out
next to qtbase.

Change-Id: I68c244c7449513d07c1e1e582de5d37c77467c20
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

tests/prebuild/license/tst_licenses.pl

@@ -578,6 +578,11 @@ sub run
     @moduleExcludedFiles = readRegularExpressionsFromFile(catfile($QT_MODULE_TO_TEST, ".qt-license-check.exclude"));
 
     my $qtbase_path = first { -d $_ } @qtbase_paths;
+    if (! $qtbase_path) {
+        my $output = `qmake -query QT_INSTALL_PREFIX/src`;
+        chomp($output);
+        $qtbase_path = $output if -d $output;
+    }
     if (! $qtbase_path) {
         fail("Cannot find qtbase module, looked at: @qtbase_paths");
         return;