Update to latest libc-0.2.68

* fill back missing NOTICE,METADATA,*LICENSE* files

Bug: 150877376
Test: make
Change-Id: I5735b22f9aade4f02ecc7b00c89ba090f7f0d786
diff --git a/METADATA b/METADATA
new file mode 100644
index 0000000..6e95b3d
--- /dev/null
+++ b/METADATA
@@ -0,0 +1,18 @@
+name: "libc"
+description: "libc provides all of the definitions necessary to easily interoperate with C code (or \"C-like\" code) on each of the platforms that Rust supports. This includes type definitions (e.g. c_int), constants (e.g. EINVAL) as well as function headers (e.g. malloc).  This crate exports all underlying platform types, functions, and constants under the crate root, so all items are accessible as libc::foo. The types and values of all the exported APIs match the platform that libc is compiled for.  More detailed information about the design of this library can be found in its associated RFC."
+third_party {
+  url {
+    type: HOMEPAGE
+    value: "https://crates.io/crates/libc"
+  }
+  url {
+    type: GIT
+    value: "https://github.com/rust-lang/libc"
+  }
+  version: "0.2.68"
+  last_upgrade_date {
+    year: 2020
+    month: 3
+    day: 20
+  }
+}