fix build on m68k with uclibc

[ffontaine]

uclibc on m68k defines pthread_spinlock_t but does not define pthread_spin_trylock so check for this function before using it

Fixes:

• http://autobuild.buildroot.org/results/0a6de11c030a4f39e402917809fc6d33fb463d1b

Signed-off-by: Fabrice Fontaine [email protected]