Merge branch 'audio-update'

Author: jtothebell

platform/libretro/Makefile.common

@@ -64,6 +64,7 @@ SOURCES_CXX := $(CORE_DIR)/platform/libretro/libretro.cpp \
                 $(CORE_DIR)/source/cart.cpp \
                 $(CORE_DIR)/source/emojiconversion.cpp \
                 $(CORE_DIR)/source/filehelpers.cpp \
+                $(CORE_DIR)/source/filter.cpp \
                 $(CORE_DIR)/source/fontdata.cpp \
                 $(CORE_DIR)/source/graphics.cpp \
                 $(CORE_DIR)/source/hostCommonFunctions.cpp \