Use ARM mode for dispatch stubs on ARMv6 and ARMv7
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.