Disconnects Store state fields from Compiler (#1761)

*  Moves CodeMemory, VMInterrupts and SignatureRegistry from Compiler
*  CompiledModule holds CodeMemory and GdbJitImageRegistration
*  Store keeps track of its JIT code
*  Makes "jit_int.rs" stuff Send+Sync
*  Adds the threads example.

Cargo.lock

@@ -2381,6 +2381,7 @@ dependencies = [
  "cc",
  "cfg-if",
  "indexmap",
+ "lazy_static",
  "libc",
  "memoffset",
  "more-asserts",