UPSTREAM: arm: provide a PCS-compliant setjmp implementation

The previous setjmp-implementation (as a static inline function that
contained an 'asm volatile' sequence) was extremely fragile: (some
v

UPSTREAM: arm: provide a PCS-compliant setjmp implementation

The previous setjmp-implementation (as a static inline function that
contained an 'asm volatile' sequence) was extremely fragile: (some
versions of) GCC optimised the set of registers. One critical example
was the removal of 'r9' from the clobber list, if -ffixed-reg9 was
supplied.

To increase robustness and ensure PCS-compliant behaviour, the setjmp
and longjmp implementation are now in assembly and closely match what
one would expect to find in a libc implementation.

Change-Id: I9403d28218f03cdf84b1e8cbd4d3d4eef790e9b9
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Tested-by: Andy Yan <andy.yan@rock-chips.com>
Signed-off-by: Andy Yan <andy.yan@rock-chips.com>

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