[hwasan] More realistic setjmp test.

Authored by fmayer on Jul 9 2021, 8:44 AM.


[hwasan] More realistic setjmp test.

The existing one actually failed on the int* p, not on int z (as can be
seen by the fault being 8 bytes rather than 4).

This is also needed to make sure the stack safety analysis does not
classify the alloca as safe.

Reviewed By: hctim

Differential Revision: https://reviews.llvm.org/D105705