Bug fix for segfault in stubs library

There was a segfault in the stubs library in posix_memalign because
of a bad parameter. The fix is to send address of the pointer as a
parameter. Also added check of result of posix_memalign.

Patch by Andrey Churbanov.

Differential Revision: http://reviews.llvm.org/D21529

llvm-svn: 273276