[Bazel] Update for 9854f2f30f (Diff library)

[GMNGeoffrey]

Summary

Updates the Bazel build for
https://github.com/llvm/llvm-project/commit/9854f2f30f by extracting a
library from llvm-diff. Note that this does not include the new
llvm-livepatch binary, for which the CMake file was added accidentally
and reverted in https://github.com/llvm/llvm-project/commit/fec8f1a008.

[GMNGeoffrey]

• Move Diff to testonly library section

utils/bazel/llvm-project-overlay/llvm/BUILD.bazel

 )
 
 cc_library(
     name = "Exegesis",
     srcs = glob([
         "tools/llvm-exegesis/lib/*.cpp",
         "tools/llvm-exegesis/lib/X86/*.cpp",
         "tools/llvm-exegesis/lib/X86/*.h",
-
         # We have to include these headers here as well as in the `hdrs` below
         # to allow the `.cpp` files to use file-relative-inclusion to find
         # them, even though consumers of this library use inclusion relative to
         # `tools/llvm-exegesis/lib` with the `strip_includes_prefix` of this
         # library. This mixture appears to be incompatible with header modules.
         "tools/llvm-exegesis/lib/*.h",
     ]),
     hdrs = glob(["tools/llvm-exegesis/lib/*.h"]),
deps = [
         ":BitReader",
         ":BitWriter",
         ":Core",
         ":Scalar",
         ":Support",
     ],
 )
 
+cc_library(
+    name = "Diff",
+    testonly = True,
+    srcs = glob(["tools/llvm-diff/lib/*.cpp"]),
+    hdrs = glob(["tools/llvm-diff/lib/*.h"]),
+    deps = [
+        ":Core",
+        ":Support",
+    ],
+)
+
 # A hacky library to expose some internal headers of gtest to its own
 # implementation source files using a stripped include prefix rather than
 # file-relative-inclusion.
 #
 # FIXME: This file should be in `textual_hdrs` instead of `hdrs`, but
 # unfortunately that doesn't work with `strip_include_prefix`:
 # https://github.com/bazelbuild/bazel/issues/12424
 #
cc_binary(
     testonly = True,
     srcs = glob([
         "tools/llvm-diff/*.cpp",
         "tools/llvm-diff/*.h",
     ]),
     copts = llvm_copts,
     stamp = 0,
     deps = [
-        ":AsmParser",
-        ":BitReader",
         ":Core",
+        ":Diff",
         ":IRReader",
         ":Support",
     ],
 )
 
 cc_binary(
     name = "llvm-isel-fuzzer",
     testonly = True,