corelib: Restore qAppFileName on OS/2.

This is needed for QProcess. Using QCoreApplication::applicationFilePath
is not correct as it requires a QCoreApplication instance which is not
required by QProcess itself. While we could still make it work on OS/2
but it's not safe too because the value returned by this method may be
changed by QCoreApplicationPrivate::setApplicationFilePath to an
arbitrary value while QProcess needs a path to the real EXE image.

src/corelib/io/qprocess_os2.cpp

@@ -95,6 +95,9 @@ QT_END_NAMESPACE
 
 QT_BEGIN_NAMESPACE
 
+// defined in qcoreapplication.cpp
+extern QString qAppFileName();
+
 #if QT_CONFIG(process)
 
 // NOTE: Copied over from qprocess_unix.cpp.
@@ -945,7 +948,7 @@ static int qt_startProcess(const QString &program, const QStringList &arguments,
             // morphing from VIO to PM which doesn't cancel the fact that we
             // are VIO from the OS/2 loader's POV.
             ULONG flags;
-            arc = DosQueryAppType(QFile::encodeName(QCoreApplication::applicationFilePath()), &flags);
+            arc = DosQueryAppType(QFile::encodeName(qAppFileName()), &flags);
             if (arc == NO_ERROR && (flags & 0x7) != FAPPTYP_WINDOWAPI) {
                 // we are originally not the PM application and thus DosExecPgm()
                 // won't be able to start PM applications directly (note that the

src/corelib/kernel/qcoreapplication.cpp

@@ -2213,6 +2213,23 @@ QString QCoreApplication::applicationDirPath()
     return d->cachedApplicationDirPath;
 }
 
+#ifdef Q_OS_OS2
+Q_CORE_EXPORT QString qAppFileName()
+{
+    char appPath[PATH_MAX + 1];
+    if (_execname(appPath, sizeof(appPath)) == 0) {
+        // _execname returns the uppercased path, try to get the real case
+        char *path = appPath;
+        char realAppPath[PATH_MAX + 1];
+        if (_realrealpath(appPath, realAppPath, sizeof(realAppPath)))
+            path = realAppPath;
+        return QFile::decodeName(path);
+    }
+
+    return QString();
+}
+#endif
+
 /*!
     Returns the file path of the application executable.
 
@@ -2249,7 +2266,7 @@ QString QCoreApplication::applicationFilePath()
     if (QCoreApplicationPrivate::cachedApplicationFilePath)
         return *QCoreApplicationPrivate::cachedApplicationFilePath;
 
-#if defined(Q_OS_WIN)
+#if defined(Q_OS_DOSLIKE)
     QCoreApplicationPrivate::setApplicationFilePath(QFileInfo(qAppFileName()).filePath());
     return *QCoreApplicationPrivate::cachedApplicationFilePath;
 #elif defined(Q_OS_MAC)
@@ -2261,17 +2278,6 @@ QString QCoreApplication::applicationFilePath()
             return *QCoreApplicationPrivate::cachedApplicationFilePath;
         }
     }
-#elif defined(Q_OS_OS2)
-    char appPath[PATH_MAX + 1];
-    if (_execname(appPath, sizeof(appPath)) == 0) {
-        // _execname returns the uppercased path, try to get the real case
-        char *path = appPath;
-        char realAppPath[PATH_MAX + 1];
-        if (_realrealpath(appPath, realAppPath, sizeof(realAppPath)))
-            path = realAppPath;
-        QCoreApplicationPrivate::setApplicationFilePath(QFileInfo(QFile::decodeName(path)).canonicalFilePath());
-        return *QCoreApplicationPrivate::cachedApplicationFilePath;
-    }
 #endif
 #if defined( Q_OS_UNIX )
 #  if defined(Q_OS_LINUX) && (!defined(Q_OS_ANDROID) || defined(Q_OS_ANDROID_EMBEDDED))