Re: JIT compiling with LLVM v10.0

Hi,

I've pushed v10.0. The big (and pretty painful to make) change is that
now all the LLVM specific code lives in src/backend/jit/llvm, which is
built as a shared library which is loaded on demand.

The layout is now as follows:

src/backend/jit/jit.c:
Part of JITing always linked into the server. Supports loading the
LLVM using JIT library.

src/backend/jit/llvm/
Infrastructure:
llvmjit.c:
General code generation and optimization infrastructure
llvmjit_error.cpp, llvmjit_wrap.cpp:
Error / backward compat wrappers
llvmjit_inline.cpp:
Cross module inlining support
Code-Gen:
llvmjit_expr.c
Expression compilation
llvmjit_deform.c
Deform compilation

I generally like how this shaped out. There's a good amount of followup
cleanup needed, but I'd appreciate some early feedback.

I've also rebased onto a recent master version.

postgres[21915][1]=# SELECT pg_llvmjit_available();
┌──────────────────────┐
│ pg_llvmjit_available │
├──────────────────────┤
│ t │
└──────────────────────┘
(1 row)

make -C src/backend/jit/llvm/ uninstall
postgres[21915][1]=# \c
You are now connected to database "postgres" as user "andres".
postgres[21922][1]=# SELECT pg_llvmjit_available();
┌──────────────────────┐
│ pg_llvmjit_available │
├──────────────────────┤
│ f │
└──────────────────────┘
(1 row)

Yeha ;)

Greetings,

Andres Freund