Arm64 Apple libs build fails, a recent regression

[sandreenko]

After #53669 the build on apple fails with:

[  0%] Building C object Native.Unix/System.Security.Cryptography.Native.Apple/CMakeFiles/System.Security.Cryptography.Native.Apple-Static.dir/pal_hmac.c.o
  /Users/seandree/git/runtime/src/libraries/Native/Unix/System.Native/pal_io.c:1491:21: error: implicit declaration of function 'preadv' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
      while ((count = preadv(fileDescriptor, (struct iovec*)vectors, (int)vectorCount, (off_t)fileOffset)) < 0 && errno == EINTR);

the command to repro:

./build.sh libs+clr -arch arm64 -c Release -runtimeconfiguration Checked

[sandreenko]

link #53669 (comment) with a possible solution from @janvorli