Avoid circularity in ENSURE-DYNAMIC-FOREIGN-SYMBOL-ADDRESS.

Use FIND-FOREIGN-SYMBOL-ADDRESS instead of FOREIGN-SYMBOL-ADDRESS,
which calls ENSURE-DYNAMIC-FOREIGN-SYMBOL-ADDRESS, for finding
"undefined_alien_function", otherwise in case undefined_alien_function
is missing for some reason, this will enter endless recursion.
Better undefined-alien-error support on ARM.

Like on x86-64, report the name of the function being missing.
call_into_c always uses R8, so use it to look up the linkage table.