compiler-rt: __aarch64_*_sync functions not available

[emaste]

Attempting to build FreeBSD with GCC 12 and in-tree compiler-rt 16 fails with:

/usr/local/bin/aarch64-unknown-freebsd13.1-ld: heimbase.pico: in function `_heim_create_type':
/tmp/cirrus-ci-build/crypto/heimdal/base/heimbase.c:281: undefined reference to `__aarch64_ldadd4_sync'
/usr/local/bin/aarch64-unknown-freebsd13.1-ld: heimbase.pico: in function `heim_retain':
/tmp/cirrus-ci-build/crypto/heimdal/base/heimbase.c:97: undefined reference to `__aarch64_ldadd4_sync'
/usr/local/bin/aarch64-unknown-freebsd13.1-ld: heimbase.pico: in function `heim_release':
/tmp/cirrus-ci-build/crypto/heimdal/base/heimbase.c:120: undefined reference to `__aarch64_ldadd4_sync'
collect2: error: ld returned 1 exit status

[jrtc27]

@sebpop compiler-rt's LSE implementation is an adaptation of libgcc's, relicensed by Linaro. Given you authored gcc-mirror/gcc@bc25483 to add them to GCC, would you be willing to relicense it as Apache-2.0 WITH LLVM-exception for inclusion within compiler-rt, please? If so I'm happy to pick up getting it through Phab.

[sebpop]

Yes, please adapt the code from my patch gcc-mirror/gcc@bc25483 to compiler-rt and please use an appropriate license for that. Thank you.

[jrtc27]

/cherry-pick 4bb2416

[llvmbot]

/branch llvm/llvm-project-release-prs/issue63483

[llvmbot]

/pull-request llvm/llvm-project-release-prs#684