Add the pooling-allocator feature.

This commit adds the `pooling-allocator` feature to both the `wasmtime` and
`wasmtime-runtime` crates.

The feature controls whether or not the pooling allocator implementation is
built into the runtime and exposed as a supported instance allocation strategy
in the wasmtime API.

The feature is on by default for the `wasmtime` crate.

Closes #3513.

crates/runtime/src/instance/allocator.rs

@@ -23,8 +23,10 @@ use wasmtime_environ::{
     SignatureIndex, TableInitializer, TrapCode, VMOffsets, WasmType, WASM_PAGE_SIZE,
 };
 
+#[cfg(feature = "pooling-allocator")]
 mod pooling;
 
+#[cfg(feature = "pooling-allocator")]
 pub use self::pooling::{
     InstanceLimits, ModuleLimits, PoolingAllocationStrategy, PoolingInstanceAllocator,
 };

crates/runtime/src/lib.rs

@@ -40,9 +40,12 @@ pub use crate::export::*;
 pub use crate::externref::*;
 pub use crate::imports::Imports;
 pub use crate::instance::{
-    InstanceAllocationRequest, InstanceAllocator, InstanceHandle, InstanceLimits,
-    InstantiationError, LinkError, ModuleLimits, OnDemandInstanceAllocator,
-    PoolingAllocationStrategy, PoolingInstanceAllocator, StorePtr,
+    InstanceAllocationRequest, InstanceAllocator, InstanceHandle, InstantiationError, LinkError,
+    OnDemandInstanceAllocator, StorePtr,
+};
+#[cfg(feature = "pooling-allocator")]
+pub use crate::instance::{
+    InstanceLimits, ModuleLimits, PoolingAllocationStrategy, PoolingInstanceAllocator,
 };
 pub use crate::jit_int::GdbJitImageRegistration;
 pub use crate::memory::{Memory, RuntimeLinearMemory, RuntimeMemoryCreator};

crates/runtime/src/memory.rs

@@ -364,6 +364,7 @@ impl Memory {
     }
 
     /// Returns whether or not the underlying storage of the memory is "static".
+    #[cfg(feature = "pooling-allocator")]
     pub(crate) fn is_static(&self) -> bool {
         if let Memory::Static { .. } = self {
             true

crates/runtime/src/table.rs

@@ -186,6 +186,7 @@ impl Table {
     }
 
     /// Returns whether or not the underlying storage of the table is "static".
+    #[cfg(feature = "pooling-allocator")]
     pub(crate) fn is_static(&self) -> bool {
         if let Table::Static { .. } = self {
             true