Revert r180739 and r180748: they broke C++11 thread_local on non-Darwin systems and did not do the right thing on Darwin.

Original commit message:

Emit the TLS intialization functions into a list.

Add the TLS initialization functions to a list of initialization functions. The
back-end takes this list and places the function pointers into the correct
section. This way they're called before `main().'

<rdar://problem/13733006>