CMakeLists: Enable checks on Clang

Enables shadow-uncaptured-locals and implicit-fallthrough for Clang.
implicit-fallthrough is not enabled by default in -Wall or -Wextra, and
shadow-uncaptured-local doesn't seem to be enabled by default by
-Wshadow, even though GCC has both of these by their respective cases.

src/CMakeLists.txt

@@ -113,6 +113,8 @@ else()
 
         $<$<CXX_COMPILER_ID:Clang>:-Wno-braced-scalar-init>
         $<$<CXX_COMPILER_ID:Clang>:-Wno-unused-private-field>
+        $<$<CXX_COMPILER_ID:Clang>:-Werror=shadow-uncaptured-local>
+        $<$<CXX_COMPILER_ID:Clang>:-Werror=implicit-fallthrough>
         $<$<CXX_COMPILER_ID:AppleClang>:-Wno-braced-scalar-init>
         $<$<CXX_COMPILER_ID:AppleClang>:-Wno-unused-private-field>
     )