Move lenType definition to runtime (partially)

src/runtime/arch_amd64.go

@@ -0,0 +1,8 @@
+// +build amd64
+
+package runtime
+
+const GOARCH = "amd64"
+
+// The length type used inside strings and slices.
+type lenType uint32

src/runtime/arch_wasm.go

@@ -0,0 +1,8 @@
+// +build wasm
+
+package runtime
+
+const GOARCH = "wasm"
+
+// The length type used inside strings and slices.
+type lenType uint32

src/runtime/hashmap.go

@@ -13,7 +13,7 @@ import (
 type hashmap struct {
 	next       *hashmap       // hashmap after evacuate (for iterators)
 	buckets    unsafe.Pointer // pointer to array of buckets
-	count      uint
+	count      lenType
 	keySize    uint8 // maybe this can store the key type as well? E.g. keysize == 5 means string?
 	valueSize  uint8
 	bucketBits uint8