Add aarch64 support

I would appreciate some hints on how to download the correct version of the toolchain depending on the host cpu architecture in `lowrisc_rv32imcb_repos`. I tried using `load("@local_config_platform//:constraints.bzl", "HOST_CONSTRAINTS")` there as well but that led to the following problem:
```
ERROR: Failed to load Starlark extension '@local_config_platform//:constraints.bzl'.
Cycle in the workspace file detected. This indicates that a repository is used prior to being defined.
The following chain of repository dependencies lead to the missing definition.
 - @local_config_platform
This could either mean you have to add the '@local_config_platform' repository with a statement like `http_archive` in your WORKSPACE file (note that transitive dependencies are not added automatically), or move an existing definition earlier in your WORKSPACE file.
ERROR: Error computing the main repository mapping: cycles detected during computation of main repo mapping
```

Author: troibe

bazelisk.sh

@@ -23,11 +23,13 @@ readonly release="v1.11.0"
 declare -A hashes=(
     # sha256sums for v1.11.0.  Update this if you update the release.
     [linux-amd64]="231ec5ca8115e94c75a1f4fbada1a062b48822ca04f21f26e4cb1cd8973cd458"
+    [linux-arm64]="f9119deb1eeb6d730ee8b2e1a14d09cb45638f0447df23144229c5b3b3bc2408"
 )
 
 declare -A architectures=(
     # Map `uname -m -o` to bazelisk's precompiled binary target names.
     [x86_64 GNU/Linux]="linux-amd64"
+    [aarch64 GNU/Linux]="linux-arm64"
 )
 
 function os_arch() {

config/compiler.bzl

@@ -10,9 +10,16 @@ load(
     "tool_path",
 )
 load("@rules_cc//cc:defs.bzl", "cc_toolchain")
+load("@local_config_platform//:constraints.bzl", "HOST_CONSTRAINTS")
+
+def _get_host_cpu():
+    cpu_constraint = "@platforms//cpu:"
+    for constraint in HOST_CONSTRAINTS:
+        if constraint.startswith(cpu_constraint):
+            return constraint[len(cpu_constraint):]
 
 PARAM_DEFAULTS = {
-    "host_system_name": "x86_64-unknown-linux-gnu",
+    "host_system_name":  _get_host_cpu() + "-unknown-linux-gnu",
     "target_system_name": "unknown",
     "target_libc": "unknown",
     "compiler": "unknown",
@@ -141,7 +148,7 @@ def setup(
     native.toolchain(
         name = "cc_toolchain_" + name,
         exec_compatible_with = [
-            "@platforms//cpu:x86_64",
+            "@platforms//cpu:" + _get_host_cpu(),
         ],
         target_compatible_with = constraints,
         toolchain = ":" + name,

toolchains/lowrisc_rv32imcb/repository.bzl

@@ -8,8 +8,8 @@ def lowrisc_rv32imcb_repos(local = None):
     http_archive_or_local(
         name = "lowrisc_rv32imcb_files",
         local = local,
-        url = "https://github.com/lowRISC/lowrisc-toolchains/releases/download/20240923-1/lowrisc-toolchain-rv32imcb-20240923-1.tar.xz",
-        sha256 = "aeea1983553f4c81c6409abcf0d6ca33b5ed4716b2b694e7ff030523cf13486a",
-        strip_prefix = "lowrisc-toolchain-rv32imcb-20240923-1",
+        url = "https://github.com/troibe/lowrisc-toolchains/releases/download/20250225-1/lowrisc-toolchain-rv32imcb-aarch64-20250225-1.tar.xz",
+        sha256 = "1b5df51abe85fb6d3cad24c62082046ab02788ef15e491040b680fcaa35a29ec",
+        strip_prefix = "lowrisc-toolchain-rv32imcb-aarch64-20250225-1",
         build_file = Label("//toolchains:BUILD.export_all.bazel"),
     )