compiler: update integer type sizes

* Use 64-bit integers on 64-bit platforms, just like gc and gccgo:
  https://golang.org/doc/go1.1#int
* Do not use a separate length type. Instead, use uintptr everywhere a
  length is expected.

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      lenType
+	count      uintptr
 	keySize    uint8 // maybe this can store the key type as well? E.g. keysize == 5 means string?
 	valueSize  uint8
 	bucketBits uint8