pgsql: Fix jit compilation bug on wide tables.

Fix jit compilation bug on wide tables.

The function generated to perform JIT compiled tuple deforming failed
when HeapTupleHeader's t_hoff was bigger than a signed int8. I'd
failed to realize that LLVM's getelementptr would treat an int8 index
argument as signed, rather than unsigned. That means that a hoff
larger than 127 would result in a negative offset being applied. Fix
that by widening the index to 32bit.

Add a testcase with a wide table. Don't drop it, as it seems useful to
verify other tools deal properly with wide tables.

Thanks to Justin Pryzby for both reporting a bug and then reducing it
to a reproducible testcase!

Reported-By: Justin Pryzby
Author: Andres Freund
Discussion: https://postgr.es/m/20181115223959.GB10913@telsasoft.com
Backpatch: 11, just as jit compilation was

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/b238527664ec6f6c9d00dba4cc2f3dab1c8b8b04

Modified Files
--------------
src/backend/jit/llvm/llvmjit_deform.c | 12 +++++++++---
src/test/regress/expected/create_table.out | 10 ++++++++++
src/test/regress/expected/sanity_check.out | 1 +
src/test/regress/sql/create_table.sql | 10 ++++++++++
4 files changed, 30 insertions(+), 3 deletions(-)