Simplify linking to different jpeg libs.

This makes it slightly more obvious which compiler should be used with
which.

Task-number: QTBUG-23119

Change-Id: Ie3e5cf995d686bfa846902a040668716c8b5f526
Reviewed-by: Andy Shaw <andy.shaw@digia.com>

src/gui/image/qjpeghandler.pri

@@ -3,8 +3,10 @@ INCLUDEPATH *= $$PWD
 HEADERS += $$PWD/qjpeghandler_p.h
 SOURCES += $$PWD/qjpeghandler.cpp
 contains(QT_CONFIG, system-jpeg) {
-    if(unix|win32-g++*): LIBS += -ljpeg
-    else:win32:          LIBS += libjpeg.lib
+    msvc: \
+        LIBS += libjpeg.lib
+    else: \
+        LIBS += -ljpeg
 } else {
     include($$PWD/../../3rdparty/libjpeg.pri)
 }