Introduce globalsym_addr.

This is an instruction used in legalization of GlobalVarData::Sym global
variables.

cranelift/filetests/isa/intel/legalize-memory.cton

@@ -29,6 +29,19 @@ ebb1(v1: i64):
     ; check: return $v2
 }
 
+function %sym() -> i64 {
+    gv0 = globalsym %something
+    gv1 = globalsym #d0bad180d0b5d182d0bed0bd
+
+ebb1:
+    v0 = global_addr.i64 gv0
+    ; check: $v0 = globalsym_addr.i64 gv0
+    v1 = global_addr.i64 gv1
+    ; check: $v1 = globalsym_addr.i64 gv1
+    v2 = bxor v0, v1
+    return v2
+}
+
 ; SpiderMonkey VM-style static 4+2 GB heap.
 ; This eliminates bounds checks completely for offsets < 2GB.
 function %staticheap_sm64(i32, i64 vmctx) -> f32 spiderwasm {