[Glacier] Move hashmap to a real hash implementation.

lib/glacier/util/hash.h

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <stdint.h>
+
+namespace glcr {
+
+// General purpose templated hash function.
+// Currently the template speciializations
+// implement FNV hashing:
+// https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
+template <typename T>
+struct Hash {
+  uint64_t operator()(const T&);
+};
+
+template <>
+struct Hash<uint64_t> {
+  uint64_t operator()(const uint64_t&);
+};
+
+class String;
+template <>
+struct Hash<String> {
+  uint64_t operator()(const String&);
+};
+
+}  // namespace glcr