libaom v3.6.1 release candidate 2

[Wan-Teh Chang]

libaom v3.6.1 release candidate 2 is available. The release tag is
v3.6.1-rc2. Your testing will be greatly appreciated.

The only difference from release candidate 1 is a new cherry-pick:
https://aomedia.googlesource.com/aom/+/9577bc1254eb13b54200b89752ae0b28091deffb

This is a bug-fix patch release for libaom v3.6.0. A main goal is to fix
the bitstream incompatibility described in
https://crbug.com/aomedia/2871#c12 quickly.

This release includes several bug fixes. This release is ABI compatible
with the last release.

- Bug Fixes
* aomedia:2871: Guard the support of the 7.x and 8.x levels for AV1
under the CONFIG_CWG_C013 config flag, and only output the 7.x and
8.x levels when explicitly requested.
* aomedia:3382: Choose sb_size by ppi instead of svc.
* aomedia:3384: Fix fullpel search limits.
* aomedia:3388: Replace left shift of xq_active by multiplication.
* aomedia:3389: Fix MV clamping in av1_mv_pred.
* aomedia:3390: set_ld_layer_depth: cap max_layer_depth to
MAX_ARF_LAYERS.
* aomedia:3418: Fix MV clamping in av1_int_pro_motion_estimation.
* aomedia:3429: Move lpf thread data init to lpf_pipeline_mt_init().
* b:266719111: Fix undefined behavior in Arm Neon code.
* b:269840681: nonrd_opt: align scan tables.
* rtc: Fix is_key_frame setting in variance partition.
* Build: Fix build with clang-cl and Visual Studio.
* Build: Fix module definition file for MinGW/MSYS.

Thanks,
Wan-Teh Chang