[ELF][ARM] Add a test that maxes out the thunk convergence limit

Add a test that takes the maximum amount of passes permitted to converge.
This will make sure that any symbol defined in a linker script gets the
correct value and that any other convergence limit involving symbol address
doesn't restrict Thunk convergence.

Differential Revision: https://reviews.llvm.org/D66346

llvm-svn: 369246