Don't cache QCoreApplication::appName.

This isn't a hot codepath, there is no gain to doing this. It introduces
unnecessary bloat (see e.g.
https://www.webkit.org/blog/2826/unusual-speed-boost-size-matters/) and
complicates boosting Qt application startup in cases where argv[0] is
overwritten.

Change-Id: I55b2b98b0de6b06fe7a049de262f3e19936b73db
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qcoreapplication.cpp

@@ -147,17 +147,13 @@ QString QCoreApplicationPrivate::macMenuBarName()
 #endif
 QString QCoreApplicationPrivate::appName() const
 {
-    static QBasicMutex applicationNameMutex;
-    QMutexLocker locker(&applicationNameMutex);
-
-    if (applicationName.isNull()) {
+    QString applicationName;
 #ifdef Q_OS_MAC
-        applicationName = macMenuBarName();
+    applicationName = macMenuBarName();
 #endif
-        if (applicationName.isEmpty() && argv[0]) {
-            char *p = strrchr(argv[0], '/');
-            applicationName = QString::fromLocal8Bit(p ? p + 1 : argv[0]);
-        }
+    if (applicationName.isEmpty() && argv[0]) {
+        char *p = strrchr(argv[0], '/');
+        applicationName = QString::fromLocal8Bit(p ? p + 1 : argv[0]);
     }
 
     return applicationName;

src/corelib/kernel/qcoreapplication_p.h

@@ -83,7 +83,6 @@ public:
     ~QCoreApplicationPrivate();
 
     QString appName() const;
-    mutable QString applicationName;
 
 #ifdef Q_OS_MAC
     static QString macMenuBarName();