Build issues on aarch64 Linux hosts

[msgilligan]

I've been trying to build OP-TEE with Rust on an aarch64 Linux host. (Mostly Debian Bookworm in a VM on MacBook M1)

I've run into at least three issues so far and made a PR for one of them:

• toolchain.mk: Rust toolchain is not downloaded on aarch64 hosts OP-TEE/build#749, with a fix PR Download Rust Toolchain during "make toolchains" on aarch64 hosts OP-TEE/build#748
• C++ tests fail on aarch64 hosts OP-TEE/build#751
• Compilation of Rust examples fails on aarch64 hosts OP-TEE/build#752

751 is not Rust-related, and is easily worked around with WITH_CXX_TESTS=n, but 752 is Rust-related and if anyone has any ideas on how to fix it, I would greatly appreciate hearing them.

[msgilligan]

We are making progress on this issue. Two of the three sub-issues above are now solved. Only OP-TEE/build#752 remains.

[msgilligan]

I have reproduced this issue by following the instructions in this project's README.md on an aarch64 Linux (Debian) machine.

See Related PR #137.

[msgilligan]

I have created a multi-architecture Dockerfile/containerFile that works correctly under AMD64 (x86_64) and exhibits the linker error we have been seeing under ARM64 (aarch64) and uploaded it in a gist:
https://gist.github.com/msgilligan/a36d61953d2caf60d33d233fed281c7b

Note that the exact error is ld.bfd: cannot find -lgcc_s: No such file or directory (In some earlier test configurations that I used the _s wasn't present.)