Fail when using cargo-zigbuild

[otavio]

Wrong build for ring:

% cargo-zigbuild b --target=arm-unknown-linux-gnueabi
   Compiling ring v0.17.8
The following warnings were emitted during compilation:

warning: [email protected]: crypto/curve25519/asm/x25519-asm-arm.S:36:1: error: invalid instruction, any one of the following would fix this:
warning: [email protected]: strd r4,[sp,#0]
warning: [email protected]: ^
warning: [email protected]: crypto/curve25519/asm/x25519-asm-arm.S:36:14: note: too few operands for instruction
warning: [email protected]: strd r4,[sp,#0]
warning: [email protected]:              ^
warning: [email protected]: crypto/curve25519/asm/x25519-asm-arm.S:36:1: note: instruction requires: armv5te
warning: [email protected]: strd r4,[sp,#0]
warning: [email protected]: ^
warning: [email protected]: crypto/curve25519/asm/x25519-asm-arm.S:36:1: note: instruction requires: thumb2
warning: [email protected]: strd r4,[sp,#0]
warning: [email protected]: ^
...

Refs: rust-cross/cargo-zigbuild#253

[briansmith]

It seems like an issue with cargo-zigbuild. This code is inherited from BoringSSL. That particular assembly file is unusual because it was written by a different person than the other ARM assembly files. There are probably workarounds in the other ARM assembly files as I see that none of them seem to use strd. We'd need somebody to contribute a fix.