Fix Qt host builds

Do not explicitly specify mkspec file when invoking qmake.
qmake itself is aware of the cross mkspec file (compiled in)
AND of the mkspec file for host builds.
Specifying it explicitly doesn't let qmake choose the
correct one and always tries to cross-compile everything.

frameworks/qt5base/files/qmake.mk

@@ -65,8 +65,6 @@ QT_HOST_LIBS:=$(QT_HOST_PREFIX)/lib
 QMAKE_SPEC:=linux-g++
 QMAKE_XSPEC:=linux-openwrt-g++
 
-QMAKE_SPECFILE:=$(QT_HOST_DATA)/mkspecs/$(QMAKE_XSPEC)
-
 PKG_INSTALL_DIR_ROOT:=$(PKG_INSTALL_DIR)
 PKG_INSTALL_DIR:=$(PKG_INSTALL_DIR_ROOT)/$(STAGING_DIR)
 
@@ -76,7 +74,6 @@ define Build/Configure/Default
 	TARGET_CXXFLAGS="$(TARGET_CPPFLAGS) $(TARGET_CXXFLAGS)" \
 	TARGET_LDFLAGS="$(TARGET_LDFLAGS)" \
 	qmake \
-		-spec $(QMAKE_SPECFILE) \
 		-o $(PKG_BUILD_DIR)/$(2)/Makefile \
 		$(PKG_BUILD_DIR)/$(2)/$(if $(1),$(1),$(PKG_NAME)).pro
 endef