qt: define QT_NO_KEYWORDS

QT_NO_KEYWORDS prevents Qt from defining the `foreach`, `signals`,
`slots` and `emit` macros.

Avoid overlap between Qt macros and boost - for example #undef hackiness
in #6421.

Conflicts:
	src/qt/addressbookpage.cpp
	src/qt/peertablemodel.cpp
	src/qt/receivecoinsdialog.cpp
	src/qt/rpcconsole.cpp

Rebased-From: d29ec6c2301e593d577126d1ca85b93307b32bf1
Github-Pull: #6433

src/qt/intro.cpp

@@ -42,10 +42,10 @@ public:
         ST_ERROR
     };
 
-public slots:
+public Q_SLOTS:
     void check();
 
-signals:
+Q_SIGNALS:
     void reply(int status, const QString &message, quint64 available);
 
 private:
@@ -102,7 +102,7 @@ void FreespaceChecker::check()
         replyStatus = ST_ERROR;
         replyMessage = tr("Cannot create data directory here.");
     }
-    emit reply(replyStatus, replyMessage, freeBytesAvailable);
+    Q_EMIT reply(replyStatus, replyMessage, freeBytesAvailable);
 }
 
 
@@ -121,7 +121,7 @@ Intro::~Intro()
 {
     delete ui;
     /* Ensure thread is finished before it is deleted */
-    emit stopThread();
+    Q_EMIT stopThread();
     thread->wait();
 }
 
@@ -277,7 +277,7 @@ void Intro::checkPath(const QString &dataDir)
     if(!signalled)
     {
         signalled = true;
-        emit requestCheck();
+        Q_EMIT requestCheck();
     }
     mutex.unlock();
 }