llvm: use default install paths

llvm: use default install paths

There was a very brittle sed hack against cpp source code
that allowed installing multiple llvm versions into the same
target/sysroot. Patching with sed is prone to silent
regressions as it can change both too little and too much,
and it indeed it broke with llvm 14. It's also difficult to tell
what the 'right' change should look like.

If this feature is actually needed somewhere, please do it properly:
proper patch and upstream first.

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>