Upstream assumes gnu99 (and has been dead for years).

Noticed while trying to bump the global default to C23.

Change-Id: I13e77540ede285a705876e7dbbdcd31e2bc898b1
diff --git a/Android.bp b/Android.bp
index 66800a7..72b9269 100644
--- a/Android.bp
+++ b/Android.bp
@@ -46,6 +46,7 @@
     ],
     unique_host_soname: true,
     host_supported: true,
+    c_std: "gnu99",
 }
 
 cc_test {
@@ -56,4 +57,5 @@
     ],
     shared_libs: ["libcn-cbor"],
     gtest: false,
+    c_std: "gnu99",
 }