i#1551 port to ARM: set plain ARM define for cpp2asm_defines
i#1551 port to ARM: set plain ARM define for cpp2asm_defines

Add missing derived define ARM for the exported cpp2asm_defines header.

Review-URL: https://codereview.appspot.com/237710043

code4bones/dynamorio,AmesianX/dynamorio,daksunt/dynamorio,bl4ckic3/dynamorio,code4bones/dynamorio,bl4ckic3/dynamorio,daksunt/dynamorio,AmesianX/dynamorio,code4bones/dynamorio,code4bones/dynamorio,code4bones/dynamorio,AmesianX/dynamorio,bl4ckic3/dynamorio,bl4ckic3/dynamorio,daksunt/dynamorio,daksunt/dynamorio,AmesianX/dynamorio,daksunt/dynamorio,bl4ckic3/dynamorio,AmesianX/dynamorio