JIT blocks for C++

[guruofquality]

Using the conf-file based registry, it should be possible to install a C++ source (or sources) and register them with a conf file. The file would describe the source locations and possible linker or include options. Upon instantiation, the JIT loader would compile the source into a module, load it, and return the resulting block to the caller.

This could be a very better way for users to write simple C++ blocks without dealing with the compiler tools. We already have a module compiler interface available, so half of the dirty work is done.

• [ ] wiki page documenting conf file and options for installing
• [x] merge the feature into master

[guruofquality]

Almost complete, a demo is checked in with comments: https://github.com/pothosware/pothos-demos/blob/master/jit_cpp_block/README.md