LLVMJIT: introduce force-inlined functions

Hi

A bunch of functions are the most used in queries. The llvmjit inlining system (tries to) get rid of the overhead of calling any function, but this is triggered only when the cost is above jit_inline_above_cost. There is thus a nice performance boost to have by choosing to "manually" inline a few specific PostgreSQL functions.
In this first patch, I've chosen to inline int4eq, int8eq and most date comparison functions.
They are definitely small, the generated code is not bigger when inlining them (surprisingly, on amd64 the code is even smaller) and are unlikely to ever change so there won't be any maintenance burden here.
On my AMD 3900XT system, this gives me a 3 to 5% performance improvement when running 1M dateeq calls.
I will likely submit a second patch version later with more functions implemented, but I thought this was an interesting first result worth discussing already.

Regards