Show the number of VMAs in the tombstone.

Tombstones (especially ones with lots of VMAs) are regularly truncated.
We can at least show the number of VMAs, though, for anyone interested
in knowing whether they got close to the default 64Ki limit.

Bug: http://b/66911122
Bug: 64709603 (presubmit balking at the line above)
Test: ran crasher, examined tombstone

(cherry picked from commit 868d39a8)

Change-Id: I286db66f28f132307d573dbe5164efc969dc6ddc