libunwind: update to 1.5.0

Cleanup Makefile for consistency with other ones.

Remove PKG_SSP. It can be fixed with -lssp_nonshared.

Add PKG_BUILD_PARALLEL for faster compilation.

Add zlib dependency. 1.5.0 requires it now.

Refresh patches.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

package/libs/libunwind/patches/002-fix-building-getcontext_S.patch

@@ -1,6 +1,5 @@
-diff -uprN a/src/mips/getcontext.S b/src/mips/getcontext.S
---- a/src/mips/getcontext.S	2012-10-06 12:54:38.000000000 +0800
-+++ b/src/mips/getcontext.S	2016-06-08 13:35:25.033051679 +0800
+--- a/src/mips/getcontext.S
++++ b/src/mips/getcontext.S
 @@ -24,12 +24,12 @@ OF CONTRACT, TORT OR OTHERWISE, ARISING
  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
  
@@ -16,4 +15,3 @@ diff -uprN a/src/mips/getcontext.S b/src/mips/getcontext.S
  #  define OFFSET 4
  # else
  #  define OFFSET 0
-