Remove global state for trap registration (#909)

* Remove global state for trap registration

There's a number of changes brought about in this commit, motivated by a
few things. One motivation was to remove an instance of using
`lazy_static!` in an effort to remove global state and encapsulate it
wherever possible. A second motivation came when investigating a
slowly-compiling wasm module (a bit too slowly) where a good chunk of
time was spent in managing trap registrations.

The specific change made here is that `TrapRegistry` is now stored
inside of a `Compiler` instead of inside a global. Additionally traps
are "bulk registered" for a module rather than one-by-one. This form of
bulk-registration allows optimizing the locks used here, where a lock is
only held for a module at-a-time instead of once-per-function.

With these changes the "unregister" logic has also been tweaked a bit
here and there to continue to work. As a nice side effect the `Compiler`
type now has one fewer field that requires actual mutability and has
been updated for multi-threaded compilation, nudging us closer to a
world where we can support multi-threaded compilation. Yay!

In terms of performance improvements, a local wasm test file that
previously took 3 seconds to compile is now 10% faster to compile,
taking ~2.7 seconds now.

* Perform trap resolution after unwinding

This avoids taking locks in signal handlers which feels a bit iffy...

* Remove `TrapRegistration::dummy()`

Avoid an case where you're trying to lookup trap information from a
dummy module for something that happened in a different module.

* Tweak some comments

crates/runtime/src/instance.rs

@@ -15,6 +15,7 @@ use crate::vmcontext::{
     VMGlobalDefinition, VMGlobalImport, VMMemoryDefinition, VMMemoryImport, VMSharedSignatureIndex,
     VMTableDefinition, VMTableImport,
 };
+use crate::TrapRegistration;
 use memoffset::offset_of;
 use more_asserts::assert_lt;
 use std::any::Any;
@@ -100,6 +101,10 @@ pub(crate) struct Instance {
     /// Handler run when `SIGBUS`, `SIGFPE`, `SIGILL`, or `SIGSEGV` are caught by the instance thread.
     pub(crate) signal_handler: Cell<Option<Box<SignalHandler>>>,
 
+    /// Handle to our registration of traps so signals know what trap to return
+    /// when a segfault/sigill happens.
+    pub(crate) trap_registration: TrapRegistration,
+
     /// Additional context used by compiled wasm code. This field is last, and
     /// represents a dynamically-sized array that extends beyond the nominal
     /// end of the struct (similar to a flexible array member).
@@ -534,6 +539,7 @@ impl InstanceHandle {
     /// safety.
     pub unsafe fn new(
         module: Arc<Module>,
+        trap_registration: TrapRegistration,
         finished_functions: BoxedSlice<DefinedFuncIndex, *const VMFunctionBody>,
         imports: Imports,
         data_initializers: &[DataInitializer<'_>],
@@ -582,6 +588,7 @@ impl InstanceHandle {
                 dbg_jit_registration,
                 host_state,
                 signal_handler: Cell::new(None),
+                trap_registration,
                 vmctx: VMContext {},
             };
             ptr::write(instance_ptr, instance);