skip test for va_copy when cross-compiling

Change-Id: I277b396b50c4e820431ec360d653e5e8b8357721

liblangtag/ExternalProject_langtag.mk

@@ -25,7 +25,7 @@ $(call gb_ExternalProject_get_state_target,langtag,build):
 		./configure --disable-modules --disable-test --disable-introspection --disable-shared --enable-static --with-pic \
 		$(if $(filter WNTMSC,$(OS)$(COM)),--disable-rebuild-data) \
 		$(if $(filter TRUE,$(HAVE_GCC_BUILTIN_ATOMIC)),"lt_cv_has_atomic=yes","lt_cv_has_atomic=no") \
-		$(if $(filter YES,$(CROSS_COMPILING)),--build=$(BUILD_PLATFORM) --host=$(HOST_PLATFORM)) \
+		$(if $(filter YES,$(CROSS_COMPILING)),--build=$(BUILD_PLATFORM) --host=$(HOST_PLATFORM) "ac_cv_va_copy=no") \
 		$(if $(filter NO,$(SYSTEM_LIBXML)),LIBXML2_CFLAGS="-I$(call gb_UnpackedTarball_get_dir,xml2)/include" \
 			LIBXML2_LIBS=$(if $(filter WNTMSC,$(OS)$(COM)),"-L$(OUTDIR)/lib -llibxml2","-L$(gb_Helper_OUTDIRLIBDIR) -lxml2"),\
 		$(if $(filter MACOSX,$(OS)),LIBXML2_CFLAGS="$(LIBXML_CFLAGS)" LIBXML2_LIBS="$(LIBXML_LIBS)")) \