alsa-utils: fix conflics with pthread.h

Backport two upstream patches to fix a build failure due to conflicts
with pthread.h:

signal.h:27: error: conflicting types for 'sin_generator_init'
./signal.h:27: error: previous declaration of 'sin_generator_init' was
here
signal.h:28: error: conflicting types for 'sin_generator_next_sample'
./signal.h:28: error: previous declaration of
'sin_generator_next_sample' was here
....

Upstream patches:

  http://git.alsa-project.org/?p=alsa-utils.git;a=commit;h=3bf8e79c3bfee3ca14277aad3d9c406dfc053bbf
  http://git.alsa-project.org/?p=alsa-utils.git;a=commit;h=ed0cce1b6061aade0077982cb5d22fa68ddffd2f

Fixes:

  http://autobuild.buildroot.net/results/b11/b114ac7a25ac95a059418b07c6cad25714d19b77/



[Peter: fix patch 0002 description]
Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>