Switch to c++11 for swiftshader.

This library depends on a snapshot of LLVM that only works with C++11.

Bug: http://b/111067277
Test: Build with default cpp_std as C++17.
Change-Id: I40de7e2357afa3c16ceac7f50241a6d0437aba09
Reviewed-on: https://swiftshader-review.googlesource.com/c/22628
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Stephen Hines <srhines@google.com>

Android.bp

diff --git a/Android.bp b/Android.bp
index f8c596f..b81c37c 100644
--- a/Android.bp
+++ b/Android.bp
@@ -30,6 +30,7 @@
     cppflags: [
         "-Woverloaded-virtual",
     ],
+    cpp_std: "c++11",
 
     target: {
         host: {