[libunwind][AArch64] Protect PC within libunwind's context. #6968

Job	Run time
stage1 (generic-cxx03, clang-19, clang++-19)	5m 47s
stage1 (generic-cxx26, clang-19, clang++-19)	11m 53s
stage1 (generic-modules, clang-19, clang++-19)	7m 51s
stage1 (generic-gcc, gcc-14, g++-14)	16m 6s
stage2 (generic-cxx11, clang-19, clang++-19)	6m 50s
macos (generic-cxx03, macos-latest)	12m 3s
stage2 (generic-cxx14, clang-19, clang++-19)	4m 58s
windows (clang-cl-dll, false)	48m 23s
macos (generic-cxx23, macos-latest)	29m 27s
stage2 (generic-cxx17, clang-19, clang++-19)	7m 47s
windows (clang-cl-static, false)	50m 45s
macos (generic-modules, macos-latest)	17m 8s
stage2 (generic-cxx20, clang-19, clang++-19)	12m 45s
windows (clang-cl-no-vcruntime, false)	49m 7s
macos (apple-configuration, macos-latest)	27m 39s
stage2 (generic-cxx23, clang-19, clang++-19)	10m 7s
windows (clang-cl-debug, false)	49m 22s
macos (apple-system, macos-13)	1h 13m 45s
stage2 (generic-gcc-cxx11, gcc-14, g++-14)	8m 30s
windows (clang-cl-static-crt, false)	52m 48s
macos (apple-system-hardened, macos-13)	50m 53s
stage2 (generic-cxx23, clang-17, clang++-17)	10m 25s
windows (mingw-dll, true)	1h 7m 25s
stage2 (generic-cxx26, clang-18, clang++-18)	13m 14s
windows (mingw-static, true)	1h 10m 1s
windows (mingw-dll-i686, true)	1h 9m 26s
windows (mingw-incomplete-sysroot, true)	7m 10s
stage3	0s
	13h 11m 35s

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