[libcalamares] Don't print funcinfo in continuations

- when a single function does more logging, it generally marks
  those as subsequent debug-messages (with Continuation, or SubEntry)
  and we don't need to print funcinfo for those, since it was already
  printed the first time.

src/libcalamares/utils/Logger.cpp

@@ -44,6 +44,10 @@ static unsigned int s_threshold =
 #endif
 static QMutex s_mutex;
 
+static const char s_Continuation[] = "\n    ";
+static const char s_SubEntry[] = " .. ";
+
+
 namespace Logger
 {
 
@@ -192,14 +196,19 @@ CDebug::~CDebug()
 {
     if ( m_funcinfo )
     {
-        m_msg.prepend( Continuation );
+        m_msg.prepend( s_Continuation );  // Prepending, so back-to-front
         m_msg.prepend( m_funcinfo );
     }
     log( m_msg.toUtf8().data(), m_debugLevel );
 }
 
-const char Continuation[] = "\n    ";
-const char SubEntry[] = " .. ";
+constexpr FuncSuppressor::FuncSuppressor( const char s[] )
+    : m_s( s )
+{
+}
+
+const constexpr FuncSuppressor Continuation( s_Continuation );
+const constexpr FuncSuppressor SubEntry( s_SubEntry );
 
 QString
 toString( const QVariant& v )

src/libcalamares/utils/Logger.h

@@ -27,8 +27,14 @@
 
 namespace Logger
 {
-DLLEXPORT extern const char Continuation[];
-DLLEXPORT extern const char SubEntry[];
+struct FuncSuppressor
+{
+    explicit constexpr FuncSuppressor( const char[] );
+    const char* m_s;
+};
+
+DLLEXPORT extern const FuncSuppressor Continuation;
+DLLEXPORT extern const FuncSuppressor SubEntry;
 
 enum
 {
@@ -47,12 +53,27 @@ public:
     explicit CDebug( unsigned int debugLevel = LOGDEBUG, const char* func = nullptr );
     virtual ~CDebug();
 
+    friend QDebug& operator<<( CDebug&&, const FuncSuppressor& );
+
 private:
     QString m_msg;
     unsigned int m_debugLevel;
     const char* m_funcinfo = nullptr;
 };
 
+inline QDebug&
+operator<<( CDebug&& s, const FuncSuppressor& f )
+{
+    s.m_funcinfo = nullptr;
+    return s << f.m_s;
+}
+
+inline QDebug&
+operator<<( QDebug& s, const FuncSuppressor& f )
+{
+    return s << f.m_s;
+}
+
 /**
  * @brief The full path of the log file.
  */