audio_core: Resolve sign conversion warnings

While were at it, we can also enable sign conversion warnings and other
common warnings as errors to prevent these from creeping back into the
codebase.

src/audio_core/CMakeLists.txt

@@ -44,6 +44,16 @@ add_library(audio_core STATIC
 
 create_target_directory_groups(audio_core)
 
+if (NOT MSVC)
+    target_compile_options(audio_core PRIVATE
+        -Werror=ignored-qualifiers
+        -Werror=implicit-fallthrough
+        -Werror=reorder
+        -Werror=sign-compare
+        -Werror=unused-variable
+    )
+endif()
+
 target_link_libraries(audio_core PUBLIC common core)
 target_link_libraries(audio_core PRIVATE SoundTouch)