Fix more cases where DSE would optimize out too many stores

GCC5/6 do aggressive dead store elimination on memory passed to
placement-new. This resulted in the Heap::Object::prototype being a
nullptr. qml.pro already contained the -fno-lifetime-dse flag, but there
are other places where we ask the memory manager to allocate data.

This is temporary band-aid, and is already fixed in 5.8.

Change-Id: Ia61a69f65fab351068a588cfc36b5b3d762ffc9f
Task-number: QTBUG-56932
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/imports/particles/particles.pro

@@ -3,6 +3,11 @@ TARGET  = particlesplugin
 TARGETPATH = QtQuick/Particles.2
 IMPORT_VERSION = 2.0
 
+greaterThan(QT_GCC_MAJOR_VERSION, 5) {
+    # Our code is bad. Temporary workaround. Fixed in 5.8
+    QMAKE_CXXFLAGS += -fno-delete-null-pointer-checks -fno-lifetime-dse
+}
+
 SOURCES += \
     plugin.cpp
 

src/quick/quick.pro

@@ -13,6 +13,11 @@ exists("qqml_enable_gcov") {
     LIBS_PRIVATE += -lgcov
 }
 
+greaterThan(QT_GCC_MAJOR_VERSION, 5) {
+    # Our code is bad. Temporary workaround. Fixed in 5.8
+    QMAKE_CXXFLAGS += -fno-delete-null-pointer-checks -fno-lifetime-dse
+}
+
 QMAKE_DOCS = $$PWD/doc/qtquick.qdocconf
 
 ANDROID_LIB_DEPENDENCIES = \

tests/auto/qml/qqmlecmascript/qqmlecmascript.pro

@@ -13,6 +13,11 @@ RESOURCES += qqmlecmascript.qrc
 
 include (../../shared/util.pri)
 
+greaterThan(QT_GCC_MAJOR_VERSION, 5) {
+    # Our code is bad. Temporary workaround. Fixed in 5.8
+    QMAKE_CXXFLAGS += -fno-delete-null-pointer-checks -fno-lifetime-dse
+}
+
 # QMAKE_CXXFLAGS = -fprofile-arcs -ftest-coverage
 # LIBS += -lgcov