Import 'proc-macro-hack' rust crate version 0.5.12

Bug: b/151760391
Test: m crosvm.experimental
Change-Id: I70ccc8c3a5640eab38ce5bcfea97feedad7e972d
diff --git a/METADATA b/METADATA
new file mode 100644
index 0000000..f5a6faa
--- /dev/null
+++ b/METADATA
@@ -0,0 +1,17 @@
+name: "proc-macro-hack"
+description:
+    "Procedural macros in expression position"
+
+third_party {
+  url {
+    type: HOMEPAGE
+    value: "https://crates.io/crates/proc-macro-hack"
+  }
+  url {
+    type: GIT
+    value: "https://github.com/dtolnay/proc-macro-hack"
+  }
+  version: "0.5.12"
+  last_upgrade_date { year: 2020 month: 3 day: 19 }
+  license_type: NOTICE
+}