[X86] Support -fno-plt __tls_get_addr calls

In general dynamic/local dynamic TLS models, with -fno-plt,

* x86: emit `calll *___tls_get_addr@GOT(%ebx)` instead of `calll ___tls_get_addr@PLT`
  Note, on x86, if we can get rid of %ebx as the PIC register,
  it may be better to use a register not preserved across function calls.
* x86_64: emit `callq *__tls_get_addr@GOTPCREL(%rip)` instead of `callq __tls_get_addr@PLT`

Reorganize the code by separating 32-bit and 64-bit.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D62106

llvm-svn: 361453