SDK: do not use FORTIFY_SOURCE flags for debug builds

If the default compiler flags have FORTIFY_SOURCE enabled, move those
to separate release variables. Otherwise debug builds will add warning:
"_FORTIFY_SOURCE requires compiling with optimization (-O)"

Change-Id: I1a9986f92e2bfe9ac0e50747276d00a73c530be3
Reviewed-by: Mikko Gronoff <mikko.gronoff@qt.io>

meta-boot2qt/classes/populate_b2qt_qt5_sdk.bbclass

@@ -56,6 +56,14 @@ EOF
     echo "QMAKE_CXXFLAGS *= ${TARGET_CC_ARCH}" >> ${SDK_DEVICE_PRI}
     echo "QMAKE_LFLAGS *= ${TARGET_CC_ARCH} ${TARGET_LDFLAGS}" >> ${SDK_DEVICE_PRI}
 
+    # Move FORTIFY_SOURCE to release flags
+    if [ -n "${lcl_maybe_fortify}" ]; then
+        sed -i -e 's/${lcl_maybe_fortify}//' ${SDK_DEVICE_PRI}
+        echo "QMAKE_CFLAGS_RELEASE *= ${lcl_maybe_fortify}" >> ${SDK_DEVICE_PRI}
+        echo "QMAKE_CXXFLAGS_RELEASE *= ${lcl_maybe_fortify}" >> ${SDK_DEVICE_PRI}
+        echo "QMAKE_LFLAGS_RELEASE *= ${lcl_maybe_fortify}" >> ${SDK_DEVICE_PRI}
+    fi
+
     # Setup qt.conf to point at the device mkspec by default
     qtconf=${SDK_OUTPUT}/${SDKPATHNATIVE}${OE_QMAKE_PATH_HOST_BINS}/qt.conf
     echo 'HostSpec = linux-g++' >> $qtconf