Pull up the following, requested by kamil in ticket #552:

external/gpl3/gcc{.old}/dist/libsanitizer/asan/asan_linux.cc 1.4
sys/arch/aarch64/include/mcontext.h            1.2
sys/arch/alpha/include/mcontext.h              1.9
sys/arch/amd64/include/mcontext.h              1.19
sys/arch/arm/include/mcontext.h                1.19
sys/arch/hppa/include/mcontext.h                1.9
sys/arch/i386/include/mcontext.h                1.14
sys/arch/ia64/include/mcontext.h                1.6
sys/arch/m68k/include/mcontext.h                1.10
sys/arch/mips/include/mcontext.h                1.22
sys/arch/or1k/include/mcontext.h                1.2
sys/arch/powerpc/include/mcontext.h            1.18
sys/arch/riscv/include/mcontext.h              1.5
sys/arch/sh3/include/mcontext.h                1.11
sys/arch/sparc/include/mcontext.h              1.14-1.17
sys/arch/sparc64/include/mcontext.h            1.10
sys/arch/vax/include/mcontext.h                1.9
tests/lib/libc/sys/Makefile                    1.50
tests/lib/libc/sys/t_ucontext.c                1.2-1.5
sys/arch/hppa/include/mcontext.h 1.10
sys/arch/ia64/include/mcontext.h 1.7

- Introduce _UC_MACHINE_FP().  _UC_MACHINE_FP() is a helper
  macro to extract from mcontext a frame pointer.
- Add new tests in lib/libc/sys/t_ucontext:
  * ucontext_sp (testing _UC_MACHINE_SP)
  * ucontext_fp (testing _UC_MACHINE_FP)
  * ucontext_pc (testing _UC_MACHINE_PC)
  * ucontext_intrv (testing _UC_MACHINE_INTRV)

Add a dummy implementation of _UC_MACHINE_INTRV() for ia64.

Implement _UC_MACHINE_INTRV() for hppa.

Make the t_ucontext.c test more portable.

We now have _UC_MACHINE_FP.

(martin)