Set sysroot for aarch64 linux llvm (#172)

After migration to `bzl_mod` some more `llvm` toolchains need to be
migrated.

Tested in `orion-engine`:
- [x] Bazel 6
- [x] Bazel 7

Author: martin4861

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

@@ -117,6 +117,8 @@ cc_toolchain_config(
     abi_version = "clang",
     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",

cc/toolchains/llvm20/aarch64-linux/BUILD.bazel

@@ -117,6 +117,8 @@ cc_toolchain_config(
     abi_version = "clang",
     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",