* This warning's wording is actually inaccurate when using the -fno-compiler-rt
  or -rtlib=none options.
* It's not all that helpful; it's already understood that these libraries are
  part of the compiler, so printing a warning is just noise. In practice, this
  warning would always happen when building upstream musl, for example.
* We don't warn when we satisfy -lunwind using our bundled libunwind either, or
  various libc libraries using our bundled libc, or when providing libc++, etc.
  So I really don't think we should be warning here either.