Remove dependency on TargetIsa from Wasmtime crates (#3178)

This commit started off by deleting the `cranelift_codegen::settings`
reexport in the `wasmtime-environ` crate and then basically played
whack-a-mole until everything compiled again. The main result of this is
that the `wasmtime-*` family of crates have generally less of a
dependency on the `TargetIsa` trait and type from Cranelift. While the
dependency isn't entirely severed yet this is at least a significant
start.

This commit is intended to be largely refactorings, no functional
changes are intended here. The refactorings are:

* A `CompilerBuilder` trait has been added to `wasmtime_environ` which
  server as an abstraction used to create compilers and configure them
  in a uniform fashion. The `wasmtime::Config` type now uses this
  instead of cranelift-specific settings. The `wasmtime-jit` crate
  exports the ability to create a compiler builder from a
  `CompilationStrategy`, which only works for Cranelift right now. In a
  cranelift-less build of Wasmtime this is expected to return a trait
  object that fails all requests to compile.

* The `Compiler` trait in the `wasmtime_environ` crate has been souped
  up with a number of methods that Wasmtime and other crates needed.

* The `wasmtime-debug` crate is now moved entirely behind the
  `wasmtime-cranelift` crate.

* The `wasmtime-cranelift` crate is now only depended on by the
  `wasmtime-jit` crate.

* Wasm types in `cranelift-wasm` no longer contain their IR type,
  instead they only contain the `WasmType`. This is required to get
  everything to align correctly but will also be required in a future
  refactoring where the types used by `cranelift-wasm` will be extracted
  to a separate crate.

* I moved around a fair bit of code in `wasmtime-cranelift`.

* Some gdb-specific jit-specific code has moved from `wasmtime-debug` to
  `wasmtime-jit`.

crates/jit/src/unwind/systemv.rs

@@ -1,11 +1,12 @@
 //! Module for System V ABI unwind registry.
 
+use crate::Compiler;
 use anyhow::{bail, Result};
 use gimli::{
     write::{Address, EhFrame, EndianVec, FrameTable, Writer},
     RunTimeEndian,
 };
-use wasmtime_environ::isa::{unwind::UnwindInfo, TargetIsa};
+use wasmtime_environ::isa::unwind::UnwindInfo;
 
 /// Represents a registry of function unwind information for System V ABI.
 pub struct UnwindRegistry {
@@ -53,7 +54,7 @@ impl UnwindRegistry {
     }
 
     /// Publishes all registered functions.
-    pub fn publish(&mut self, isa: &dyn TargetIsa) -> Result<()> {
+    pub fn publish(&mut self, compiler: &Compiler) -> Result<()> {
         if self.published {
             bail!("unwind registry has already been published");
         }
@@ -63,7 +64,7 @@ impl UnwindRegistry {
             return Ok(());
         }
 
-        self.set_frame_table(isa)?;
+        self.set_frame_table(compiler)?;
 
         unsafe {
             self.register_frames();
@@ -74,9 +75,9 @@ impl UnwindRegistry {
         Ok(())
     }
 
-    fn set_frame_table(&mut self, isa: &dyn TargetIsa) -> Result<()> {
+    fn set_frame_table(&mut self, compiler: &Compiler) -> Result<()> {
         let mut table = FrameTable::default();
-        let cie_id = table.add_cie(match isa.create_systemv_cie() {
+        let cie_id = table.add_cie(match compiler.compiler().create_systemv_cie() {
             Some(cie) => cie,
             None => bail!("ISA does not support System V unwind information"),
         });

crates/jit/src/unwind/winx64.rs

@@ -1,7 +1,8 @@
 //! Module for Windows x64 ABI unwind registry.
 
+use crate::Compiler;
 use anyhow::{bail, Result};
-use wasmtime_environ::isa::{unwind::UnwindInfo, TargetIsa};
+use wasmtime_environ::isa::unwind::UnwindInfo;
 use winapi::um::winnt;
 
 /// Represents a registry of function unwind information for Windows x64 ABI.
@@ -49,7 +50,7 @@ impl UnwindRegistry {
     }
 
     /// Publishes all registered functions.
-    pub fn publish(&mut self, _isa: &dyn TargetIsa) -> Result<()> {
+    pub fn publish(&mut self, _compiler: &Compiler) -> Result<()> {
         if self.published {
             bail!("unwind registry has already been published");
         }