cranelift: add i64.{ishl,ushr,ashr} libcalls.

These libcalls are useful for 32-bit platforms.

On x86_32 in particular, commit 4ec16fa0 added support for legalizing
64-bit shifts through SIMD operations. However, that legalization
requires SIMD to be enabled and SSE 4.1 to be supported, which is not
acceptable as a hard requirement.

crates/runtime/src/libcalls.rs

@@ -98,6 +98,21 @@ pub extern "C" fn wasmtime_i64_srem(x: i64, y: i64) -> i64 {
     x % y
 }
 
+/// Implementation of i64.ishl
+pub extern "C" fn wasmtime_i64_ishl(x: i64, y: i64) -> i64 {
+    x << y
+}
+
+/// Implementation of i64.ushr
+pub extern "C" fn wasmtime_i64_ushr(x: u64, y: i64) -> u64 {
+    x >> y
+}
+
+/// Implementation of i64.sshr
+pub extern "C" fn wasmtime_i64_sshr(x: i64, y: i64) -> i64 {
+    x >> y
+}
+
 /// Implementation of f64.ceil
 pub extern "C" fn wasmtime_f64_ceil(x: f64) -> f64 {
     x.ceil()