Some of the aeabi functions were missing PACBTI support. The lack of it
resulted in exceptions at runtime if the running environment had PAC
and/or BTI enabled.
This patch adds this support. This involves the addition of PACBTI
instructions, depending on whether each of these features is enabled,
plus the saving and restoring of the PAC code that resides in r12. Some
of the common code has been put in preprocessor macros to reduce
duplication, but not all, especially since some register saving and
restoring is very specific to each context.
a59a8ae1a9