Upgrade to GCC 4.8 for Linux standalone build.

This patch modifies android-configure.sh to use the prebuilt 4.8
Linux host toolchain when available.

+ Fix a few sources to get rid of ugly compiler warnings.

Note: this works best with the following patch for the GPU
      emulation libraries:

      https://android-review.googlesource.com/#/c/92482/1

Change-Id: I7ae1c6cf2d58c2902affa36886bfa87956da622d
5 files changed