Add Linux AArch64 Bazel support and simplify. (#3422)

There was a lot of repetition and unnecessary cruft in our Bazel
toolchain support. Switch to generating all of it with a single macro
that handles everything. This should make no real difference but
dramatically simplifies adding a new CPU.

Use this simplified system and add `aarch64` which is how Arm 64-bit CPU
support shows up on a Linux host.

Also teach the basic scripts to map `aarch64` to `arm64` which is used
in the released artifact strings.

scripts/scripts_utils.py

@@ -149,6 +149,8 @@ def _get_machine() -> str:
     machine = platform.machine()
     if machine == "x86_64":
         machine = "amd64"
+    elif machine == "aarch64":
+        machine = "arm64"
     return machine