Update llvm to 15.0.6 (#237)

Author: Kelwan

WORKSPACE.bazel

@@ -203,9 +203,9 @@ hedron_compile_commands_setup()
 
 http_archive(
     name = "com_grail_bazel_toolchain",
-    sha256 = "7fa5a8624b1148c36e09c7fa29ef6ee8b83f865219c9c219c9125aac78924758",
-    strip_prefix = "bazel-toolchain-c3131a6894804ee586d059c57ffe8e88d44172e1",
-    url = "https://github.com/grailbio/bazel-toolchain/archive/c3131a6894804ee586d059c57ffe8e88d44172e1.zip",
+    sha256 = "3cf5ac4bb7dae3776da586fe85685274f5d89cbb59436f50f572928354e72198",
+    strip_prefix = "bazel-toolchain-70a0fb556662fe3cadb07da32c91e232eb0d883d",
+    url = "https://github.com/grailbio/bazel-toolchain/archive/70a0fb556662fe3cadb07da32c91e232eb0d883d.zip",
 )
 
 load("@com_grail_bazel_toolchain//toolchain:deps.bzl", "bazel_toolchain_dependencies")
@@ -217,7 +217,8 @@ load("@com_grail_bazel_toolchain//toolchain:rules.bzl", "llvm_toolchain")
 llvm_toolchain(
     name = "llvm_toolchain",
     cxx_standard = {"linux": "c++20"},
-    llvm_version = "14.0.0",
+    distribution = "clang+llvm-15.0.6-x86_64-linux-gnu-ubuntu-18.04.tar.xz",
+    llvm_version = "15.0.6",
 )
 
 load("@llvm_toolchain//:toolchains.bzl", "llvm_register_toolchains")