[runtimes] Revert the libc++ __config_site change

This is a massive revert of the following commits (from most revent to oldest):

	2b9b7b5775a1d8fcd7aa5abaa8fc0bc303434f1a.
	529ac33197f6408952ae995075ac5e2dc5287e81
	28270234f1478047e35879f4ba8838b47edfcc14
	69c2087283cf7b17ca75f69daebf4ffc158b754a
	b5aa67446e01bd277727b05710a42e69ac41e74b
	5d796645d6c8cadeb003715c33e231a8ba05b6de

After checking-in the __config_site change, a lot of things started breaking
due to widespread reliance on various aspects of libc++'s build, notably the
fact that we can include the headers from the source tree, but also reliance
on various "internal" CMake variables used by the runtimes build and compiler-rt.

These were unintended consequences of the change, and after two days, we
still haven't restored all the bots to being green. Instead, now that I
understand what specific areas this will blow up in, I should be able to
chop up the patch into smaller ones that are easier to digest.

See https://reviews.llvm.org/D89041 for more details on this adventure.

GitOrigin-RevId: 48e4b0fd3a3d68cc9774699964cf4c6c2be38cf3
1 file changed
tree: 4c0ed60b87b29945387ce6801033942ddca2d711
  1. .clang-format
  2. CMakeLists.txt
  3. LICENSE.TXT
  4. cmake/
  5. docs/
  6. include/
  7. src/
  8. test/