Pass --wrap=pthread_create to linker for -fsplit-stack.

From

https://gcc.gnu.org/ml/gcc-patches/2010-09/msg01807.html

-fsplit-stack should pass --wrap=pthread_create to linker for -fsplit-stack
It is needed to initialize the stack guard.  This fixes PR 20148.

Patch by H.J Lu!

llvm-svn: 258698