Add subtract_neon.c
- vp8_subtract_b_neon
- vp8_subtract_mby_neon
- vp8_subtract_mbuv_neon

Change-Id: If9a17a093478552e3e3276eeaa3f098b9021d08c
Signed-off-by: James Yu <james.yu@linaro.org>

_t is reserved by posix

+ switch to camelcase
  http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml#Type_Names

Change-Id: Ic738b97d492f244c58989a0f73a4d763340ec274

used to wrap API functions to ensure full environment consistency as
opposed to the renamed ASM_REGISTER_STATE_CHECK which is used with
assembly functions.
currently checks the FPU tag word in x86/x86_64 gcc builds to ensure
emms has been called.

Change-Id: Ie241772dbf903d33d516a1add4c8c6783f2e1490

Allow selectively building just the intrinsics for armv8

Change-Id: I2f29b2e4508b8b8e5649c2906b3159ad1d4ec477

Change-Id: I6d8ac50ce842749a2a643d8173bbd301cc284236

Change-Id: I7ee89d6fc2afc20563d1784598ce83e29c0e6651

Change-Id: I826655a708010149de231ca31a2e3ba4f1842c0c

Suggested by James Zern to clear out cpplint warnings for all unit
test code.

Change-Id: I731a3fa4d2a257eb9ef733426ba84286fbd7ea34

Change-Id: If908328c1dbbb5bd84c57e30fab1cda1804933e4

add ClearSystemState() to reset MMX registers avoiding corrupting
subsequent tests.

Change-Id: I668deb09aa7aa467709776e5819f936910698bc0

Change-Id: I69d00bfd1b10c03581838b15cd9a6dd66f4fa416

Change-Id: Ib8f8a66c9fd31e508cdc9caa662192f38433aa3d

Patch Set 1: gain familiarity with unit tests... added simple
4x4 subtract test
Patch Set 2: fixed mistakes, parameterized as suggested
Patch Set 3: randomized the source/predictor data


Change-Id: I33432bdf7c9f2a9b8c2533a37106382c2a8209ee
Signed-off-by: Scott LaVarnway <slavarnway@google.com>