Add -std=gnu11 to compiler.c.flags in platform.txt
Add -std=gnu11 to compiler.c.flags in platform.txt

Related to issue #221

facchinm/corelibs-arduino101,eriknyquist/corelibs-arduino101,yashaswini-hanji/corelibs-arduino101,SidLeung/corelibs-arduino101,sandeepmistry/corelibs-arduino101,eriknyquist/corelibs-arduino101,sgbihu/corelibs-arduino101,bigdinotech/corelibs-arduino101,SidLeung/corelibs-arduino101,sgbihu/corelibs-arduino101,yashaswini-hanji/corelibs-arduino101,01org/corelibs-arduino101,linrjing/corelibs-arduino101,sandeepmistry/corelibs-arduino101,facchinm/corelibs-arduino101,yashaswini-hanji/corelibs-arduino101,sandeepmistry/corelibs-arduino101,01org/corelibs-arduino101,linrjing/corelibs-arduino101,01org/corelibs-arduino101,bigdinotech/corelibs-arduino101,sgbihu/corelibs-arduino101,bigdinotech/corelibs-arduino101