Merge pull request #4596 from FearlessTobi/port-5495

Port citra-emu/citra#5495: "Add LGTM static analyzer config file"

.lgtm.yml

+path_classifiers:
+  library: "externals"
+extraction:
+  cpp:
+    prepare:
+      packages:
+      - "libsdl2-dev"
+      - "qtmultimedia5-dev"
+      - "clang-format-10"
+      - "libtbb-dev"
+      - "libjack-jackd2-dev"
+      - "doxygen"
+      - "graphviz"