When checking find_package() components, special case qtmain.

Its just a library on Windows only.
Fixes bug #11791.

Modules/FindQt4.cmake

@@ -1112,7 +1112,13 @@ IF( Qt4_FIND_COMPONENTS )
   SET(_QT4_FOUND_REQUIRED_VARS QT_QMAKE_EXECUTABLE QT_MOC_EXECUTABLE QT_RCC_EXECUTABLE QT_INCLUDE_DIR QT_LIBRARY_DIR)
   FOREACH( component ${Qt4_FIND_COMPONENTS} )
     STRING( TOUPPER ${component} _COMPONENT )
-    SET(_QT4_FOUND_REQUIRED_VARS ${_QT4_FOUND_REQUIRED_VARS} QT_${_COMPONENT}_INCLUDE_DIR QT_${_COMPONENT}_LIBRARY)
+    if(${_COMPONENT} STREQUAL "QTMAIN")
+      IF(Q_WS_WIN)
+        SET(_QT4_FOUND_REQUIRED_VARS ${_QT4_FOUND_REQUIRED_VARS} QT_${_COMPONENT}_LIBRARY)
+      ENDIF(Q_WS_WIN)
+    else(${_COMPONENT} STREQUAL "QTMAIN")
+      SET(_QT4_FOUND_REQUIRED_VARS ${_QT4_FOUND_REQUIRED_VARS} QT_${_COMPONENT}_INCLUDE_DIR QT_${_COMPONENT}_LIBRARY)
+    endif(${_COMPONENT} STREQUAL "QTMAIN")
   ENDFOREACH( component )
 
   if(Qt4_FIND_COMPONENTS MATCHES QtGui)