title: unrecognized property "cflags" for cc_prebuilt_library_shared module
body: <p>I am writing <code>Android.bp</code> file for one of the prebuild library. In <code>Android.mk</code> It was possible to add CFlags for prebuilt library; however same is not working in case of blueprint i.e. <code>Android.bp</code>. A snippet of what I am doing is below:</p>
  
  <pre><code>cc_prebuilt_library_shared {
      name: "samplelib",
      vendor_available:true,
      cflags: [
         "-Wall",
          "-Wextra",
          "-Werror",
      ],
      tags: [
          "optional",
          "eng",
          "debug",
      ],
  
      target: {
          android_x86:{
                   srcs: ["bin/x86/samplelib.so"],
                   compile_multilib: "32",
                   relative_install_path: "lib",
          },
          android_x86_64:{
                   srcs: ["bin/x86_64/samplelib.so"],
                   compile_multilib: "64",
                   relative_install_path: "lib64",
          },
     },
  }
  </code></pre>
  
  <p>However I am getting following error:</p>
  
  <pre><code>/Android.bp:5:11: unrecognized property "cflags"
  </code></pre>
  
  <p>So if I understand correctly, <code>cflags</code> can't be used with <code>cc_prebuilt_library_shared</code> module; if that's the case how can we enable <code>CFlags</code> for this module then ? </p>