Consume less memory with relocations

https://github.com/FEX-Emu/FEX/blob/b5ae9e4c976fd2c542502e48c3e734c7bdd0e089/External/FEXCore/Source/Interface/Core/ObjectCache/Relocations.h#L72

Currently relocations use a union which causes them all to be 48 bytes in size.
We can save a bit of allocation overhead by not using a union. Thunks are significantly less common than the other relocations, which means that 16 (or 10 when packed) ends up being quite a bit smaller than 48.