Fix amalgamation by changing include style for structdef.int.h.
Fix amalgamation by changing include style for structdef.int.h.

tempbottle/upb,tbetbetbe/upb,tbetbetbe/upb,tbetbetbe/upb,bsn069/upb,tbetbetbe/upb,bsn069/upb,tbetbetbe/upb,tempbottle/upb,tempbottle/upb,tempbottle/upb,bsn069/upb,bsn069/upb,tempbottle/upb,bsn069/upb