package/libiqrf: fix static link

- libiqrf depends on pthread, so add a patch fixing the build-system that way
- disable shared object build when BR2_PREFER_STATIC_LIB is set

Fixes:
  http://autobuild.buildroot.net/results/210/2108f37e4a41af0b527c78e646e82f1cafa0353d/



Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>