Load llvm-as and llc from PATH
Remove old LLVM types file
Introduce new data structure that the JIT needs access to

The JIT needs to be told about certain fields so we can do faster checks
for whether we have any interrupts scheduled or the stack overflows.
This refactor allows for teaching the JIT about this structure without
having to know the total VM layout, which is fairly complicated.
Update LLVM type information for new VMJIT information
Use run_gc_soon method
Make interrupt checks in the JIT cheaper

We use the new VMJIT structure to read whether we have an interrupt
scheduled for this thread and check the status of whether we have to GC
from shared state.

Improves performance of for example Integer#gcd, because that checks
interrupts in the loop.

Before:
=== ./bin/rbx ===
Fixnum gcd Fixnum => Fixnum
                      3232489.4 (±3.7%) i/s -   16153410 in   5.004410s

After:
=== bin/rbx ===
Fixnum gcd Fixnum => Fixnum
                      3846171.8 (±2.4%) i/s -   19263285 in   5.011503s
Add benchmark for Integer#gcd