This changes the ARMv7 dispatch stubs to use ARM mode instead of Thumb.
The same instructions actually work either way, with the only difference being the
_GLOBAL_OFFSET_TABLE_ offsets at the end. Since we have the stubs 128-byte aligned, using ARM doesn't actually make the binary any larger, either.
Using ARM, though, means that the dispatch stubs can work for ARMv6 as well.