MacroExpander: Prevent loop with subproviders

Prevent a loop where a subprovider of a macroexpander creates
the macroexpander itself.

Change-Id: Id2f3e29651aeb22c818091d8c785a6ea01545463
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/utils/stringutils.cpp

@@ -31,6 +31,7 @@
 
 #include <QDir>
 #include <QRegularExpression>
+#include <QSet>
 
 #include <limits.h>
 
@@ -153,7 +154,8 @@ bool AbstractMacroExpander::expandNestedMacros(const QString &str, int *pos, QSt
                 *pos = i;
                 return true;
             }
-            if (resolveMacro(varName, ret)) {
+            QSet<AbstractMacroExpander*> seen;
+            if (resolveMacro(varName, ret, seen)) {
                 *pos = i;
                 if (!pattern.isEmpty() && currArg == &replace) {
                     const QRegularExpression regexp(pattern);