It's already in qt5.14

src/kmime_dateformatter.cpp

@@ -235,11 +235,7 @@ QByteArray DateFormatterPrivate::zone(time_t t)
     QTextStream s(&ret, QIODevice::WriteOnly);
     s << (neg ? '-' : '+')         
       << qSetFieldWidth(2) << qSetPadChar(QLatin1Char('0'))
-     #if (QT_VERSION < QT_VERSION_CHECK(5, 15, 0))
-      << right
-     #else
       << Qt::right
-     #endif
       << hours << mins;
     //old code: ret.sprintf( "%c%.2d%.2d", (neg) ? '-' : '+', hours, mins );
 

src/kmime_header_parsing.cpp

@@ -1457,11 +1457,7 @@ static void decodeRFC2231Value(KCodecs::Codec *&rfc2231Codec,
     if (!dec->decode(decCursor, decEnd, bit, bend)) {
         KMIME_WARN << rfc2231Codec->name()
                    << "codec lies about its maxDecodedSizeFor()"
-              #if (QT_VERSION < QT_VERSION_CHECK(5, 15, 0))
-                   << endl
-              #else
                    << Qt::endl
-              #endif
                    << "result may be truncated";
     }
 

src/kmime_headers.cpp

@@ -423,11 +423,7 @@ bool MailboxList::parse(const char *&scursor, const char *const send,
         if (!(it).displayName.isEmpty()) {
             KMIME_WARN << "mailbox groups in header disallowing them! Name: \""
                        << (it).displayName << "\""
-              #if (QT_VERSION < QT_VERSION_CHECK(5, 15, 0))
-                       << endl
-              #else
                        << Qt::endl
-              #endif
                           ;
         }
         d->mailboxList += (it).mailboxList;
@@ -453,12 +449,7 @@ bool SingleMailbox::parse(const char *&scursor, const char *const send,
 
     if (d->mailboxList.count() > 1) {
         KMIME_WARN << "multiple mailboxes in header allowing only a single one!"
-              #if (QT_VERSION < QT_VERSION_CHECK(5, 15, 0))
-                   << endl
-              #else
-                   << Qt::endl
-              #endif
-                      ;
+                   << Qt::endl;
     }
     return true;
 }
@@ -665,12 +656,7 @@ bool Token::parse(const char *&scursor, const char *const send, bool isCRLF)
     if (scursor != send) {
         KMIME_WARN << "trailing garbage after token in header allowing "
                    "only a single token!"
-              #if (QT_VERSION < QT_VERSION_CHECK(5, 15, 0))
-                   << endl
-              #else
-                   << Qt::endl
-              #endif
-                      ;
+                   << Qt::endl;
     }
     return true;
 }
@@ -818,12 +804,7 @@ bool DotAtom::parse(const char *&scursor, const char *const send,
     if (scursor != send) {
         KMIME_WARN << "trailing garbage after dot-atom in header allowing "
                    "only a single dot-atom!"
-              #if (QT_VERSION < QT_VERSION_CHECK(5, 15, 0))
-                   << endl
-              #else
-                   << Qt::endl
-              #endif
-                      ;
+                   << Qt::endl;
     }
     return true;
 }
@@ -1096,12 +1077,7 @@ bool SingleIdent::parse(const char *&scursor, const char *const send,
     if (d->msgIdList.count() > 1) {
         KMIME_WARN << "more than one msg-id in header "
                    << "allowing only a single one!"
-              #if (QT_VERSION < QT_VERSION_CHECK(5, 15, 0))
-                   << endl
-              #else
-                   << Qt::endl
-              #endif
-                      ;
+                   << Qt::endl;
     }
     return true;
 }
@@ -1176,13 +1152,7 @@ bool ReturnPath::parse(const char *&scursor, const char *const send,
         // check that there was no display-name:
         if (maybeMailbox.hasName()) {
             KMIME_WARN << "display-name \"" << maybeMailbox.name()
-                       << "\" in Return-Path!"
-              #if (QT_VERSION < QT_VERSION_CHECK(5, 15, 0))
-                       << endl
-              #else
-                       << Qt::endl
-              #endif
-                          ;
+                       << "\" in Return-Path!" << Qt::endl;
         }
     }
     d->mailbox = maybeMailbox;
@@ -1192,12 +1162,7 @@ bool ReturnPath::parse(const char *&scursor, const char *const send,
     // and warn if it wasn't:
     if (scursor != send) {
         KMIME_WARN << "trailing garbage after angle-addr in Return-Path!"
-              #if (QT_VERSION < QT_VERSION_CHECK(5, 15, 0))
-                   << endl
-              #else
-                   << Qt::endl
-              #endif
-                      ;
+                   << Qt::endl;
     }
     return true;
 }