Cranelift CLIF-level differential fuzzer (#3038)

* cranelift: Initial fuzzer implementation

* cranelift: Generate multiple test cases in fuzzer

* cranelift: Separate function generator in fuzzer

* cranelift: Insert random instructions in fuzzer

* cranelift: Rename gen_testcase

* cranelift: Implement div for unsigned values in interpreter

* cranelift: Run all test cases in fuzzer

* cranelift: Comment options in function_runner

* cranelift: Improve fuzzgen README.md

* cranelift: Fuzzgen remove unused variable

* cranelift: Fuzzer code style fixes

Thanks! @bjorn3

* cranelift: Fix nits in CLIF fuzzer

Thanks @cfallin!

* cranelift: Implement Arbitrary for TestCase

* cranelift: Remove gen_testcase

* cranelift: Move fuzzers to wasmtime fuzz directory

* cranelift: CLIF-Fuzzer ignore tests that produce traps

* cranelift: CLIF-Fuzzer create new fuzz target to validate generated testcases

* cranelift: Store clif-fuzzer config in a separate struct

* cranelift: Generate variables upfront per function

* cranelift: Prevent publishing of fuzzgen crate

Cargo.lock

@@ -640,6 +640,16 @@ dependencies = [
  "target-lexicon",
 ]
 
+[[package]]
+name = "cranelift-fuzzgen"
+version = "0.75.0"
+dependencies = [
+ "anyhow",
+ "arbitrary",
+ "cranelift",
+ "rand 0.8.3",
+]
+
 [[package]]
 name = "cranelift-interpreter"
 version = "0.75.0"
@@ -747,6 +757,7 @@ dependencies = [
  "cranelift-entity",
  "cranelift-filetests",
  "cranelift-frontend",
+ "cranelift-fuzzgen",
  "cranelift-interpreter",
  "cranelift-jit",
  "cranelift-module",
@@ -3676,6 +3687,9 @@ name = "wasmtime-fuzz"
 version = "0.0.0"
 dependencies = [
  "cranelift-codegen",
+ "cranelift-filetests",
+ "cranelift-fuzzgen",
+ "cranelift-interpreter",
  "cranelift-reader",
  "cranelift-wasm",
  "libfuzzer-sys",