configure: fix llc detection on recent Debian
Where clang --version was returning:
clang version 9.0.1-15+b1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Newer version like clang-10 on Debian are returning:
Debian clang version 10.0.1-8+b1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
As a result the parsing was failing to determine which llc was
available on the system.
Ticket: #6598
(cherry picked from commit
37b1595c20959353ec438860dc5a49bcae227aa8)