Enable cfg(gc_zeal) when fuzzing (#13053)

Author: fitzgen

Cargo.toml

@@ -214,6 +214,9 @@ check-cfg = [
   'cfg(pulley_disable_interp_simd)',
   'cfg(arc_try_new)',
 
+  # Activated by `cargo fuzz` when building for fuzzing.
+  'cfg(fuzzing)',
+
   # When enabled, `cfg(gc_zeal)` activates aggressive GC debugging assertions.
   'cfg(gc_zeal)',
 ]

crates/cranelift/build.rs

@@ -0,0 +1,5 @@
+fn main() {
+    if cfg!(fuzzing) {
+        println!("cargo:rustc-cfg=gc_zeal");
+    }
+}

crates/wasmtime/build.rs

@@ -34,6 +34,7 @@ fn main() {
     custom_cfg("has_virtual_memory", has_virtual_memory);
     custom_cfg("has_custom_sync", has_custom_sync);
     custom_cfg("has_host_compiler_backend", has_host_compiler_backend);
+    custom_cfg("gc_zeal", cfg!(fuzzing));
 
     // If this OS isn't supported and no debug-builtins or if Cranelift doesn't support
     // the host or there's no need to build these helpers.