pgsql: Don't generate tuple deforming functions for virtual slots.

Don't generate tuple deforming functions for virtual slots.

Virtual tuple table slots never need tuple deforming. Therefore, if we
know at expression compilation time, that a certain slot will always
be virtual, there's no need to create a tuple deforming routine for
it.

Author: Andres Freund
Discussion: https://postgr.es/m/20181105210039.hh4vvi4vwoq5ba2q@alap3.anarazel.de

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/7ef04e4d2cb287e4e28b87f24b4b36ef4e07530b

Modified Files
--------------
src/backend/jit/llvm/llvmjit_deform.c | 7 ++++++-
src/backend/jit/llvm/llvmjit_expr.c   | 1 +
src/include/jit/llvmjit.h             | 4 +++-
3 files changed, 10 insertions(+), 2 deletions(-)