examples/rust-async: Block native32 due to unclear build issues

Author: chrysn

examples/lang_support/official/rust-async/Makefile

@@ -27,4 +27,7 @@ DEVELHELP ?= 1
 # Change this to 0 show compiler invocation lines by default:
 QUIET ?= 1
 
+# TODO: Unclear alignment issues
+BOARD_BLACKLIST := native32
+
 include $(RIOTBASE)/Makefile.include