explicit casting to int64_t for literal value

Bug: 292304818
Test: build for darwin
Change-Id: I678e0c73dfa7b8cc83315f157e7602c9913d306e
diff --git a/src/build.cc b/src/build.cc
index 3f6bb81..a682bcd 100644
--- a/src/build.cc
+++ b/src/build.cc
@@ -681,7 +681,7 @@
       auto acc = p.second;
 
       if (!e) {
-        return std::make_pair(0L, std::unordered_map<Edge*, int64_t>());
+        return std::make_pair((int64_t)0, std::unordered_map<Edge*, int64_t>());
       }
       auto run = weight_getter(e);
       auto new_priority = run + acc;