configure: add work around for gcc-4.9 aarch64 bug

add -frename-registers to avoid:
src/dsp/dec_neon.c:1234:1: internal
compiler error: in simplify_const_unary_operation, at
simplify-rtx.c:1539

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62040
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61622
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=757738

Change-Id: I52fb3a29ac30b82b27da05378bdb495ddebb97d7
Merge "configure: add work around for gcc-4.9 aarch64 bug"
MIPS: dspr2: added optimization for (un)filters

HorizontalFilter
VerticalFilter
GradientFilter
HorizontalUnfilter
VerticalUnfilter
GradientUnfilter

Change-Id: I54055b4767c37719691811072e95bf79c1f627b1
Add smart RGB->YUV conversion option -pre 4

New function: WebPPictureSmartARGBToYUVA()
This implement smart RGB->YUV conversion.

This is rather undocumented for now, and is triggered using '-pre 4'
preprocessing option.

This is slow-ish and use quite some memory, but should be improvable.
This is somehow a usable beta version.

Change-Id: Ia50a8c30134e4cab8a7d3eb70aef13ce1f6187a1
Merge "Add smart RGB->YUV conversion option -pre 4"