Migrate x86_64-aarch64-linux toolchain

Author: martin4861

cc/toolchains/llvm/x86_64-aarch64-linux/BUILD.bazel

@@ -101,7 +101,12 @@ cc_toolchain_config(
     name = "local-x86_64-aarch64-linux",
     abi_libc_version = "glibc_unknown",
     abi_version = "clang",
-    builtin_sysroot = "external/aarch64-sysroot",
+    builtin_sysroot = select({
+        "@rules_swiftnav//cc:_use_libcpp": None,
+        # Remove once bzlmod is enabled by default
+        "@rules_swiftnav//cc:_enable_bzlmod": "external/rules_swiftnav++swift_cc_toolchain_extension+aarch64-sysroot",
+        "//conditions:default": "external/aarch64-sysroot",
+    }),
     compiler = "clang",
     cxx_builtin_include_directories = [
         "%sysroot%/usr/include",

cc/toolchains/llvm/x86_64-aarch64-linux/wrappers/wrapper

@@ -35,6 +35,7 @@ fi
 
 tool_name=$(basename "${BASH_SOURCE[0]}")
 toolchain_bindir=external/x86_64-linux-llvm/bin
+toolchain_bindir_as_bzlmod="external/rules_swiftnav++swift_cc_toolchain_extension+x86_64-linux-llvm/bin"
 
 if [[ -f "${toolchain_bindir}"/"${tool_name}" ]]; then
   # We're running under _execroot_, call the real tool.