fate: generate tests/pixfmts.mak for all targets requiring it

All subtargets which should run the fate-filter-pixdesc% need to
generate and include tests/pixfmts.mak. Most noteable missing target was
fate itself.
configure: check $as first before using $gas as GNU as

llvm's integrated assembler supports the AArch64 asm on darwin since
August 2014. So check $as first before using gas-preprocessor.pl via
$gas. Makes the checks specific for that the architecture specific asm
needs. PPC Altivec and AArch64 needs on ':vararg' for macro arguments.
Arm needs in addition the '.altmacro' directive.
wmalosslessdec: fix mclms_coeffs* array size

Fixes corruption of context

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC:libav-stable@libav.org
Bug-Id: CVE-2014-2098
Signed-off-by: Anton Khirnov <anton@khirnov.net>
Merge commit 'd395895cdb2ac8c95bd488549e7f893bd4dcc248'

* commit 'd395895cdb2ac8c95bd488549e7f893bd4dcc248':
  fate: generate tests/pixfmts.mak for all targets requiring it

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '15201e256035a3e8f9d3d7b96fc327467e1a8ead'

* commit '15201e256035a3e8f9d3d7b96fc327467e1a8ead':
  configure: check $as first before using $gas as GNU as

Conflicts:
	configure

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '849b9d34c7ef70b370c53e7af3940f51cbc07d0f'

* commit '849b9d34c7ef70b370c53e7af3940f51cbc07d0f':
  wmalosslessdec: fix mclms_coeffs* array size

See: ec9578d54d09b64bf112c2bf7a34b1ef3b93dbd3
Merged-by: Michael Niedermayer <michaelni@gmx.at>
avutil: add pixelutils API
build: remove wrong avcodec dep in decimate

This was probably a mistake with mpdecimate. The decimate filter doesn't
depend on avcodec.
avfilter/deshake: remove avcodec dependency
avfilter/mp_decimate: remove avcodec dependency
avfilter/select: remove optional avcodec dependency
avfilter/select: fix "t" eval variable comment