Refactor TLS code and add some tests. The tests and expected results are:

 pic |  declaration | linkage  | visibility |

!pic |  declaration | external | default    | tls1.ll     tls2.ll     | local exec
 pic |  declaration | external | default    | tls1-pic.ll tls2-pic.ll | general dynamic
!pic | !declaration | external | default    | tls3.ll     tls4.ll     | initial exec
 pic | !declaration | external | default    | tls3-pic.ll tls4-pic.ll | general dynamic

!pic |  declaration | external | hidden     | tls7.ll     tls8.ll     | local exec
 pic |  declaration | external | hidden     | X                       | local dynamic
!pic | !declaration | external | hidden     | tls9.ll     tls10.ll    | local exec
 pic | !declaration | external | hidden     | X                       | local dynamic

!pic |  declaration | internal | default    | tls5.ll     tls6.ll     | local exec
 pic |  declaration | internal | default    | X                       | local dynamic

The ones marked with an X have not been implemented since local dynamic is not implemented.

llvm-svn: 65632