diff -uNr qt-everywhere-opensource-src-4.6.3_orig/qmake/project.cpp qt-everywhere-opensource-src-4.6.3/qmake/project.cpp
--- qt-everywhere-opensource-src-4.6.3_orig/qmake/project.cpp	2010-06-02 09:03:09.000000000 +0700
+++ qt-everywhere-opensource-src-4.6.3/qmake/project.cpp	2010-07-31 19:44:43.767000035 +0700
@@ -1482,6 +1482,14 @@
     }
 
     vars = base_vars; // start with the base
+    QByteArray var = qgetenv("QMAKE_IGNORE_PREDEFINED_CFLAGS");
+    if(var.isNull())
+    {
+        vars["QMAKE_CFLAGS_RELEASE"].clear();
+        vars["QMAKE_CFLAGS_DEBUG"].clear();
+        vars["QMAKE_CXXFLAGS_RELEASE"].clear();
+        vars["QMAKE_CXXFLAGS_DEBUG"].clear();
+    }
 
     //get a default
     if(pfile != "-" && vars["TARGET"].isEmpty())