Merge #18779: doc: Better explain GNU ld's dislike of ld64's options

cd24f37ea9168bd56b8c518ea6125e242cc4213d doc: Better explain GNU ld's dislike of ld64's options (fanquake)

Pull request description:

  There's also now more than a single option being special cased for
  darwin. If we didn't special case these options they would still end
  up on the link line and the binaries produced would just segfault.

  I'm going to plug #17874 here as well, because adding
  `-fatal-warnings` to our `AX_CHECK_LINK_FLAG` calls would
  mostly prevent this sort of option mangling from happening.

  An example of the warning behaviour:
  ```bash
  echo "int main() {}" | g++ -x c++ -std=c++11 -Wl,-dead_strip -
  /usr/bin/ld: warning: cannot find entry symbol ad_strip; defaulting to 0000000000001040

  nm -C a.out
  0000000000001000 t _init
  0000000000001040 T _start
                   U ad_strip
  ```

ACKs for top commit:
  dongcarl:
    ACK cd24f37ea9168bd56b8c518ea6125e242cc4213d

Tree-SHA512: 8c5ff11b647e7d44dbb3f509a07caf8606a6b481c114403f0de72b3ad65395dbe9a3436e731ae1b46a823431ed23c3c6aacab8942d78629d59cd8c258c5dbf02

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