Allow building with Clang 13

[mbautin]

Some changes that were necessary for Clang 13:

• libc++ and libc++abi now need to be built together because libc++abi needs access to libc++ headers
• For building libc++ and libc++abi under TSAN, a compiler wrapper hack turned out to be necessary to allow building shared objects that still have undefined TSAN-related symbols.

Other improvements:

• Better display of long CMake command lines (breaking CMake arguments that are themselves compiler or argument lists into separate lines).

[spolitov]

Do we need all those build variants?

[mbautin]

Yes, I would like to have Clang 12 and 13 available with both types of LTO, as well as without LTO, and with/without of Linuxbrew. Also I think maintaining two versions of Clang (the "production" one, which is 12 at the moment, and the next one) is useful.

[svarnau]

LGTM