Consider passing through TARGET_CC & TARGET_AR in Cross.toml for rustls

[phated]

According to the ring (dependency of rustls), the TARGET_CC and TARGET_AR env variables are required to cross-compile it.

Our cross-compilation seems fine, but we might want to provide these in the Cross.toml file. 🤷

[target.x86_64-unknown-linux-gnu.env]
passthrough = [
    "TARGET_CC=x86_64-linux-gnu-gcc",
    "TARGET_AR=x86_64-linux-gnu-ar",
]

[target.x86_64-unknown-linux-musl.env]
passthrough = [
    "TARGET_CC=x86_64-linux-musl-gcc",
    "TARGET_AR=x86_64-linux-musl-ar",
]

[target.aarch64-unknown-linux-gnu.env]
passthrough = [
    "TARGET_CC=aarch64-linux-gnu-gcc",
    "TARGET_AR=aarch64-linux-gnu-ar",
]

[target.aarch64-unknown-linux-musl.env]
passthrough = [
    "TARGET_CC=aarch64-linux-musl-gcc",
    "TARGET_AR=aarch64-linux-musl-ar",
]

[phated]

Ref noir-lang/build-nargo#3

[kevaundray]

Now that we have moved the contents of this to noir-lang -- should we transfer over this issue?

[Savio-Sou]

We might skip this piece if we're taking #2275 on (?)

Assigning P-LOW as it seems like the work is not blocking other efforts.

Guessing E-LOW.