commit 98e1f847b11ab5b5b307514095f942ae8592862e
author Leonard Chan <leonardchan@google.com> Thu Oct 03 17:25:33 2019 -0700
committer Leonard Chan <leonardchan@google.com> Thu Oct 03 17:40:19 2019 -0700
tree ec4a1b2483d24727657f986075433efe389edb44
parent 57dd611f3cc47cc702627e912f4bb80d1c95d372

Make vboot_version extern in header

When enabling `-fno-common` in Fuchsia, we get a bunch of linker errors
when linking futility:

```
ld.lld: error: duplicate symbol: vboot_version
>>> defined at futility.h:43 (../../third_party/vboot_reference/futility/futility.h:43)
>>>            host_x63-asan_no_detect_leaks/obj/third_party/vboot_reference/futility/futility.cmd_bdb.c.o:(vboot_version)
>>> defined at futility.h:43 (../../third_party/vboot_reference/futility/futility.h:43)
>>>            host_x64-asan_no_detect_leaks/obj/third_party/vboot_reference/futility/futility.cmd_create.c.o:(.bss.vboot_version+0x0)
```

and think this is because -fno-common places vboot_version for
unitialized global variables in the BSS section of each object file.
Making it extern instead resolves each reference to its definition in
futility/misc.c.

Change-Id: Ibc0ea747918569d0c854e7d2ee838e7537442eee