fix: install aarch64-apple-darwin toolchain on x86 (#421)

We always create universal binaries when compiling on x86. This means
that the aarch64-apple-darwin also needs to be installed. Install that
toolchain automatically if it doesn't exist yet.

This change has also been tested for the case when the toolchain already
exists. In that case it just reports:

    info: component 'rust-std' for target 'aarch64-apple-darwin' is up to date

Thanks @lanzafame for reporting this issue.

Author: vmx

.circleci/config.yml

@@ -103,7 +103,6 @@ jobs:
       - prepare:
           linux: false
           darwin: true
-      - run: cd rust && rustup target add aarch64-apple-darwin
       - run: cd rust && cargo fetch
       - run: cd rust && cargo install cargo-lipo
       - build_project

install-filcrypto

@@ -163,6 +163,10 @@ build_from_source() {
     # Note that the cross compile works on x86_64 for m1, but doesn't work on m1.
     # For m1, we will build natively if building from source.
     if [ "$(uname -s)" = "Darwin" ] && [ "$(uname -m)" = "x86_64" ]; then
+        # Rustup only installs the correct versions for the current
+        # architecture you're on. As we cross-compile to aarch64, we need to
+        # make sure that toolchain is installes as well.
+        rustup target add aarch64-apple-darwin
         build="lipo"
         additional_flags="--targets x86_64-apple-darwin,aarch64-apple-darwin "
     else