android: gallium/auxiliary: drop log2/log2f redefitions

android: gallium/auxiliary: drop log2/log2f redefitions

Recent versions of bionic has picked up support for these functions,
leading to build issues due to the redefition of the symbols.

Note: wrapping things in #ifdef does not cut it :\

Identical patch is available in chromium, android-x86 and perhaps other
projects.

    commit 66c1c789ce3407472de9ed620c9f815639058835
    Author: rmcilroy@chromium.org
    Date:   Wed Apr 02 10:59:34 2014 +0000

        Porting to x64 Android. Remove redefinitions of log2 and log2f.

        BUG=
        R=kbr@chromium.org

        Review URL: https://codereview.chromium.org/216773005

    commit 9cc0a0d2b0499556680b182888af86f29d4ec30b
    Author: Chih-Wei Huang <cwhuang@linux.org.tw>
    Date:   Sun Jul 21 23:04:19 2013 +0800

        android: remove log2, log2f

        The functions are already defined in the latest bionic.

Cc: Chia-I Wu <olvaffe@gmail.com>
Cc: "10.1 10.2" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Acked-by: Chia-I Wu <olvaffe@gmail.com>