This change adds initial support for range extension thunks. All thunks must
be created within the first pass so some corner cases are not supported. A
follow up patch will add support for multiple passes.
With this change the existing tests arm-branch-error.s and
arm-thumb-branch-error.s now no longer fail with an out of range branch.
These have been renamed and tests added for the range extension thunk.
Differential Revision: https://reviews.llvm.org/D34691
llvm-svn: 316752