Enable libunwind for rtems #1170

Job	Run time
iOS (aarch64-apple-ios, iphoneos)	15s
Docker (aarch64-unknown-linux-gnu)	38s
iOS (x86_64-apple-ios, iphonesimulator)	14s
Docker (arm-unknown-linux-gnueabihf)	34s
Docker (armv7-unknown-linux-gnueabihf)	47s
Docker (i586-unknown-linux-gnu)	31s
Windows AArch64	58s
Test (ubuntu-24.04, stable)	2m 3s
Docker (i686-unknown-linux-gnu)	31s
Test (ubuntu-24.04, beta)	2m 6s
Docker (powerpc64-unknown-linux-gnu)	41s
Test (ubuntu-24.04, nightly)	2m 23s
Docker (s390x-unknown-linux-gnu)	35s
Build Targets (wasm32-unknown-unknown)	16s
Docker (x86_64-pc-windows-gnu)	49s
Test (macos-latest, stable)	1m 1s
Build Targets (wasm32-wasip1)	15s
Docker (x86_64-unknown-linux-gnu)	27s
Test (macos-latest, nightly)	1m 33s
Build Targets (x86_64-unknown-fuchsia)	17s
Docker (x86_64-unknown-linux-musl)	28s
Test (windows-latest, stable-x86_64-msvc)	1m 57s
Docker (arm-linux-androideabi)	1m 25s
Test (windows-latest, stable-i686-msvc)	1m 58s
Build Targets (x86_64-fortanix-unknown-sgx)	15s
Docker (armv7-linux-androideabi)	1m 42s
Miri	2m 41s
Test (windows-latest, stable-x86_64-gnu)	2m 3s
Build Targets (x86_64-unknown-illumos)	17s
Docker (aarch64-linux-android)	1m 15s
Test (windows-latest, nightly-x86_64-msvc)	1m 20s
Docker (i686-linux-android)	1m 17s
Test (windows-latest, nightly-i686-msvc)	2m 1s
MSRV (ubuntu-24.04)	14s
Docker (x86_64-linux-android)	1m 8s
Rustfmt	6s
Test (windows-latest, nightly-x86_64-gnu)	2m 13s
MSRV (windows-latest)	32s
	39m 46s

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