[C++][Gandiva] Generate Filter kernels from gandiva code at compile time

[asfimport]

The goal of this feature is to support generating kernels at compile time (and possibly runtime if gandiva is linked) to avoid rewriting C++ kernels that gandiva knows how to compile. The generated kernels would be linked in the compute module.

This is an experimental task that will guide future development, notably implementing aggregate kernels in gandiva once instead both C++ and gandiva implementations.

Reporter: Francois Saint-Jacques / @fsaintjacques

Subtasks:

• [C++][Gandiva] Add DumpIR to Filter/Projector classes
• [C++][Gandiva] Add CMake support for compiling LLVM's IR into a library
• [Gandiva] Add support for literal variables

_{Note: This issue was originally created as ARROW-7818. Please see the migration documentation for further details.}