Add graviton2 and graviton3 for llvm20

Author: martin4861

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

@@ -115,7 +115,7 @@ cc_toolchain_config(
         "//conditions:default": [],
     }),
     host_system_name = X86_64_LINUX,
-    target_cpu = "k8",
+    target_cpu = "k8",  # this should be aarch64?
     target_libc = "glibc_unknown",
     target_system_name = AARCH64_LINUX,
     tool_paths = {
@@ -125,7 +125,7 @@ cc_toolchain_config(
         "gcov": "wrappers/llvm-profdata",
         "llvm-cov": "wrappers/llvm-cov",
         "llvm-profdata": "wrappers/llvm-profdata",
-        "ld": "wrappers/ld.ldd",
+        "ld": "wrappers/ld.ldd",  # This should be ld.lld?
         "nm": "wrappers/llvm-nm",
         "objcopy": "wrappers/llvm-objcopy",
         "objdump": "wrappers/llvm-objdump",

cc/toolchains/llvm20/x86_64-aarch64-linux/BUILD.bazel

@@ -102,13 +102,18 @@ cc_toolchain_config(
     abi_libc_version = "glibc_unknown",
     abi_version = "clang",
     builtin_sysroot = select({
-        # _use_libcpp case needs to be implemented properly here!
+        "@rules_swiftnav//cc:_use_libcpp": None,
         "//conditions:default": "external/rules_swiftnav++swift_cc_toolchain_extension+aarch64-sysroot",
     }),
     compiler = "clang",
     cxx_builtin_include_directories = [
         "%sysroot%/usr/include",
     ],
+    extra_copts = select({
+        "@rules_swiftnav//cc/constraints:graviton2": ["-mcpu=neoverse-n1"],
+        "@rules_swiftnav//cc/constraints:graviton3": ["-mcpu=neoverse-512tvb"],
+        "//conditions:default": [],
+    }),
     host_system_name = X86_64_LINUX,
     target_cpu = "aarch64",
     target_libc = "glibc_unknown",
@@ -158,3 +163,39 @@ toolchain(
     toolchain = ":cc-clang-x86_64-aarch64-linux",
     toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
 )
+
+toolchain(
+    name = "cc-toolchain-aarch64-bullseye-graviton2",
+    exec_compatible_with = [
+        "@platforms//cpu:x86_64",
+        "@platforms//os:linux",
+    ],
+    target_compatible_with = [
+        "@platforms//os:linux",
+        "@platforms//cpu:aarch64",
+        "@rules_swiftnav//cc/constraints:glibc_2_31",
+        "@rules_swiftnav//cc/constraints:graviton2",
+        "@rules_swiftnav//cc/constraints:llvm20_toolchain",
+    ],
+    target_settings = None,
+    toolchain = ":cc-clang-x86_64-aarch64-linux",
+    toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
+)
+
+toolchain(
+    name = "cc-toolchain-aarch64-bullseye-graviton3",
+    exec_compatible_with = [
+        "@platforms//cpu:x86_64",
+        "@platforms//os:linux",
+    ],
+    target_compatible_with = [
+        "@platforms//os:linux",
+        "@platforms//cpu:aarch64",
+        "@rules_swiftnav//cc/constraints:glibc_2_31",
+        "@rules_swiftnav//cc/constraints:graviton3",
+        "@rules_swiftnav//cc/constraints:llvm20_toolchain",
+    ],
+    target_settings = None,
+    toolchain = ":cc-clang-x86_64-aarch64-linux",
+    toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
+)

platforms/BUILD.bazel

@@ -212,6 +212,32 @@ platform(
     visibility = ["//visibility:public"],
 )
 
+platform(
+    name = "aarch64_bullseye_llvm20_graviton2",
+    constraint_values = [
+        "@platforms//os:linux",
+        "@platforms//cpu:aarch64",
+        "@rules_swiftnav//cc/constraints:graviton2",
+        "@rules_swiftnav//cc/constraints:glibc_2_31",
+        "@rules_swiftnav//cc/constraints:llvm20_toolchain",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+platform(
+    name = "aarch64_bullseye_llvm20_graviton3",
+    constraint_values = [
+        "@platforms//os:linux",
+        "@platforms//cpu:aarch64",
+        "@rules_swiftnav//cc/constraints:graviton3",
+        "@rules_swiftnav//cc/constraints:glibc_2_31",
+        "@rules_swiftnav//cc/constraints:llvm20_toolchain",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+# GCC system
+
 platform(
     name = "x86_64_linux_gcc11_system",
     constraint_values = [