pgsql: jit: Fix type used for Datum values in LLVM IR.

jit: Fix type used for Datum values in LLVM IR.

Commit 2a600a93 made Datum 8 bytes wide everywhere. It was no longer
appropriate to use TypeSizeT on 32 bit systems, and JIT compilation
would fail with various type check errors. Introduce a separate
LLVMTypeRef with the name TypeDatum. TypeSizeT is still used in some
places for actual size_t values.

Reported-by: Dmitry Mityugov <d(dot)mityugov(at)postgrespro(dot)ru>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Tested-by: Dmitry Mityugov <d(dot)mityugov(at)postgrespro(dot)ru>
Discussion: https://postgr.es/m/0a9f0be59171c2e8f1b3bc10f4fcf267%40postgrespro.ru

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0951942bba25f85ad29a4f096ed51a356652b5a2

Modified Files
--------------
src/backend/jit/llvm/llvmjit.c | 2 +
src/backend/jit/llvm/llvmjit_deform.c | 10 +--
src/backend/jit/llvm/llvmjit_expr.c | 150 +++++++++++++++++-----------------
src/backend/jit/llvm/llvmjit_types.c | 1 +
src/include/jit/llvmjit.h | 1 +
src/include/jit/llvmjit_emit.h | 11 ++-
6 files changed, 94 insertions(+), 81 deletions(-)