configure: Do not use pthread_create to check for pthread

Certain instrumentation addons leads to a false positive in configure
and link failures at the end of the build phase.

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
dcadec: Add some logging before returning on error

Based on a patch by Michael Niedermayer.

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
gitignore: Ignore multilibrary example programs
doc: Try to find nonstandard Perl path from the environment
dsputil: x86: Move ff_inv_zigzag_direct16 table init to mpegvideo

The table is MMX-specific and used nowhere else.
build: Add shorthand for HOSTCC compile macro
build: Add rule for building host-specific object files
dv: Move DV VLC data tables out of header file
dv: Split off DV video encoder into its own file
alsa-audio-dec: explicitly cast the delay to a signed int64

Otherwise the expression will be evaluated as unsigned, which will break
when the result should be negative.
CC:libav-stable@libav.org
avconv: initialize hwaccel_pix_fmt

Fixes an assertion failure in vdpau_get_buffer() when -hwaccel auto is
used, but hwaccel init fails.
configure: Add detected C library and host compiler to informative output
configure: Detect msvcrt libc with a CPP check instead of a link check

Simplifies host/target libc detection splitting.
attributes: Use __declspec(noreturn) on MSVC

For any future use of av_noreturn.