build, qt: Fix QMAKE_CXXFLAGS expression for mingw32 host

Author: hebasto

depends/packages/qt.mk

@@ -171,7 +171,7 @@ $(package)_config_opts_mingw32 += -no-freetype
 $(package)_config_opts_mingw32 += -xplatform win32-g++
 $(package)_config_opts_mingw32 += "QMAKE_CFLAGS = '$($(package)_cflags) $($(package)_cppflags)'"
 $(package)_config_opts_mingw32 += "QMAKE_CXX = '$($(package)_cxx)'"
-$(package)_config_opts_mingw32 += "QMAKE_CXXFLAGS = '$($(package)_cflags) $($(package)_cppflags)'"
+$(package)_config_opts_mingw32 += "QMAKE_CXXFLAGS = '$($(package)_cxxflags) $($(package)_cppflags)'"
 $(package)_config_opts_mingw32 += "QMAKE_LFLAGS = '$($(package)_ldflags)'"
 $(package)_config_opts_mingw32 += -device-option CROSS_COMPILE="$(host)-"
 $(package)_config_opts_mingw32 += -pch