Erik de Castro Lopo authored Jun 22, 2019 and Ben Gamari committed Jun 25, 2019

LLVM version numberinf changed recently. Previously, releases were numbered
4.0, 5.0 and 6.0 but with version 7, they dropped the redundant ".0".

Fix requires for Llvm detection and some code.

(cherry picked from commit 71aca77c)