[bazel] Remove -lm on macOS (llvm#86706)

Bazel links this library by default which leads to this linker warning on macOS: ``` ld: warning: ignoring duplicate libraries: '-lm' ```

Author: keith

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

@@ -292,6 +292,10 @@ cc_library(
  "-ldl",
  "-lm",
  ],
+ "@platforms//os:macos": [
+ "-pthread",
+ "-ldl",
+ ],
  "//conditions:default": [
  "-pthread",
  "-ldl",