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>