C_C_A animal on HEAD gets stuck in initdb

Hello,

my CLOBBER_CACHE_ALWAYS animal, jaguarundi, has gotten stuck in "make
check"'s initdb three times in a row now.

I have trace output covering about the final minute of initdb. It mainly
consists of ~90000 iterations of

- Open base/1/1259 [pg_class]
- Seek to end [twice]
- Open global/pg_filenode.map
- Read 512 bytes
- Close global/filenode.map
- Open base/1/pg_filenode.map
- Read 512 bytes
- Close base/1/pg_filenode.map
- Close base/1/1259

with some operations on other heap files in between. At the very end, it
writes 8K of zeros to 1259_fsm at offset 0x10000, then it starts waiting
on a semaphore and never finishes.

If someone would like the 0.5 GiB of trace output (FreeBSD ktrace), it
compresses to 1.75 MiB.

All the best,

--
Christian