Try to make LGTM work again

Author: KitsuneRal

.lgtm.yml

@@ -8,7 +8,9 @@ extraction:
     prepare:
       packages: # Assuming package base of eoan
       - qtmultimedia5-dev
-#    after_prepare:
+      - g++-10
+    after_prepare:
+      - export CC="gcc-10" CXX="g++-10"
 #    - git clone https://gitlab.matrix.org/matrix-org/olm.git
 #    - pushd olm
 #    - cmake . -Bbuild -GNinja