Commit
0eb1c35ed7e08e11de5f71e4aaece17e0e566319
by Oliver Smithgcc/Makefile: fail early if xxd is not installed
Since aaec8734 ("add fw update crcstub") the xxd program is required for
running the Makefile.
Change-Id: I6a3e7021929ba58c14f1ffced5702d2dfa839ebe