bash: Compile with gnu89 for legacy K&R compatibility

Change-Id: I39f03998b141ae4a20fd578c91d9839792c6bda2
diff --git a/Android.bp b/Android.bp
index d307e28..013ccd3 100644
--- a/Android.bp
+++ b/Android.bp
@@ -154,6 +154,7 @@
         "-Wno-int-conversion",
         "-Wno-missing-field-initializers",
     ],
+    c_std: "gnu89",
     local_include_dirs: [
         "include",
         "lib",