kconfig: fix make xconfig when gettext is missing

The C-based config programs are properly guarded from a missing (or,
currently, external) libintl.h by the HOST_EXTRACFLAGS check, but
this does not help the C++-based qconf.
Signed-off-by: Yaakov Selkowitz <yselkowi@redhat.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/kconfig/Makefile

@@ -206,6 +206,7 @@ always := dochecklxdialog
 
 # Add environment specific flags
 HOST_EXTRACFLAGS += $(shell $(CONFIG_SHELL) $(srctree)/$(src)/check.sh $(HOSTCC) $(HOSTCFLAGS))
+HOST_EXTRACXXFLAGS += $(shell $(CONFIG_SHELL) $(srctree)/$(src)/check.sh $(HOSTCXX) $(HOSTCXXFLAGS))
 
 # generated files seem to need this to find local include files
 HOSTCFLAGS_zconf.lex.o	:= -I$(src)