libc_r spintrylock patch

[Venkatesh Srinivas]

Hi,A patch to libc_r, to add _spintrylock(). spintrylock is used by nmalloc; if you LD_PRELOAD libc_r, you will fall down to libthread_xu's spintrylock, which is not good behavior.

http://endeavour.zapto.org/dfly/libc_r_spintrylock.diff-- vs