use -mx32, as travis use x86 version of linux gcc

tests/project.yml

@@ -42,7 +42,7 @@
   #  1) remove the trailing [] from the :common: section
   #  2) add entries to the :common: section (e.g. :test: has TEST defined)
   :commmon: &common_defines 
-    - MCU=MCU_LPC43XX -std=gnu99 -m32
+    - MCU=MCU_LPC43XX -std=gnu99 -mx32
     - CORE_M4
     - __CODE_RED
     - _TINY_USB_SOURCE_FILE_