[compiler-rt] Return correct size of struct pthread for glibc-2.12.2
[compiler-rt] Return correct size of struct pthread for glibc-2.12.2

There seems to be a difference between 2.12.1 and 2.12.2 in 64-bit build.
Tested on Scientific Linux 6.6, based on RHEL.

Differential Revision: http://reviews.llvm.org/D17190

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@261193 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt