Fix sigsetjmp/siglongjmp to save/restore RT signals on arm/x86 too.

Our arm and x86 ABIs shipped with a 32-bit `sigset_t`, so we need to
use sigprocmask64 to save/restore the RT signals too. (This is important
because several are in use by the system, and the behavior of our 32-bit
`sigset_t` is to clear the RT signals.)

Bug: http://b/72493232
Test: ran tests
Change-Id: Idff91f8b2849276e5a3073d07eccd84e02a34410