build: Fix ASan build & silence Clang 15 warnings

[varungandhi-src]

Context:

• It seems like grailbio/bazel-toolchain doesn't natively support sanitizers. Adding support for cross compilation, CUDA, and sanitizers bazel-contrib/toolchains_llvm#90
• After fixing an Abseil related error about a missed dependency on ignore files, I ran into a problem where the rpaths in the ASan-ified binary were:

  @executable_path
  external/llvm_toolchain_llvm/lib/clang/15.0.6/lib/darwin
  

  The second path is incorrect, because the path is not from the root of the project.
• So I've added the hack for the rpath so that it finds the asan runtime correctly. Initially, I was looking into if we could link ASan statically, but the LLVM binary release only has dylibs for macOS, no static archives. This comment pointed out the rpath hack + the necessity to have a dylib. Support cc_toolchain specifying runtime dynamic libraries bazelbuild/bazel#16309 (comment)