android_webview: Build against NDK prebuilts, not system libraries.

android_webview: Build against NDK prebuilts, not system libraries.

To allow the chromium WebView to build unbundled, we need to stop
linking to system libraries and instead link to the prebuilt libraries
in the NDK.

This change rolls gyp to include the required makefile generation
changes, and adjusts the chromium side to match:

1) Stop setting use_system_stlport and instead use the NDK stlport by
   specifying LOCAL_NDK_STL_VARIANT := stlport_static

2) Remove support for the use_system_stlport flag entirely as WebView
   was the only user.

3) Don't try to link standard libraries like -lc -lm as the NDK does
   this automatically.

4) Don't include the OpenAL headers from frameworks/wilhelm; these are
   already part of the NDK with no special include path needed.

BUG=409851

Review URL: https://codereview.chromium.org/571953002

Cr-Commit-Position: refs/heads/master@{#300212}