This patch enables integrating orc::LLJIT with the ORCv2 platforms (MachOPlatform and ELFNixPlatform) and the compiler-rt orc runtime. Changes include:
- Adding SPS wrapper functions for the orc runtime's dlfcn emulation functions, allowing initialization and deinitialization to be invoked by LLJIT
- Changing the LLJIT code generation default to add UseInitArray so that .init_array constructors are generated for ELF platforms
- Integrating the ORCv2 Platforms into lli, and adding a PlatformSupport implementation to the LLJIT instance used by lli which implements initialization and deinitialization by calling the new wrapper functions in the runtime.
- Should the ORCPlatformSupport class included in lli be moved into LLJIT?
- The integration test for Darwin explicitly sets -relocation-model=pic when invoking lli so that a __DATA,__mod_init_func section is generated; if this is not done the default code generation options use the static relocation mode, which causes a __TEXT, __constructor to be generated, and the runtime does not deal with these. Might there be a better way to handle this?